/ 


r.^o 


\S 


Issued  December  31,  1913, 

HAWAII  AGRICULTURAL  EXPERIMENT  STATION, 

E.  V.  WILCOX,  Special  Agent  in  Charge. 


Bulletin  No.  30. 


THE  EFFECT  OF  HEAT  ON 
HAWAIIAN  SOILS. 


BY 


W.  P.  KELLEY, 


Chemist, 


AND 


UNIV.  OF  Fl 
DOCUMENTS  DFPT 


WILLIAM  McGEORGE 

Assistant  Chemist. 


> 


DEPOSITORY 


UNDER  THE  SUPERVISION  OF 
OFFICE    OF    EXPERIMENT    STATIC 

U,  8.   DEPARTMENT  OF  AGRICULTURE 


***** 


~.<"' 


WASHINGTON: 

GOVERNMENT  PRINTING  OFFICE. 

1913. 


Issued  Decern ber  31,  1913, 

HAWAII  AGRICULTURAL  EXPERIMENT  STATION, 

E.  V.  WILCOX,  Special  Agent  in  Charge. 


Bulletin  No.   30. 


THE  EFFECT  OF  HEAT  ON 
HAWAIIAN  SOILS. 


BY 


W.  P.  KELLEY, 

Chemist, 


AND 


WILLIAM  McGEORGE, 

Assistant  Chemist. 


UNDER   THE  SUPERVISION   OF 
OFFICE    OF    EXPERIMENT    STATIONS, 

U.   S.    DEPARTMENT  OF   AGRICULTURE. 


WASHINGTON: 

GOVERNMENT  PRINTING  OFFICE. 

1913. 


HAWAII  AGRICULTURAL    EXPERIMENT  STATION,  HONOLULU. 

[Under  the  supervision  of  A.  C.  True,  Director  of  the  Office  of  Experiment  Stations, 
United  States  Department  of  Agriculture.] 

Walter  H.  Evans,  Chief  of  Division  of  Insular  Stations,  Office  of  Experiment  Stations. 

STATION   STAFF. 

E.  V.  Wilcox,  Special  Agent  in  Charge. 
J.  Edgar  Higgins,  Horticulturist. 

W.  P.  Kelley,  Chemist. 

C.  K.  McClelland,  Agronomist. 

D.  T.  Full  aw  ay,  Entomologist. 

W.  T.  McGeorge,  Assistant  Chemist. 
Alice  R.  Thompson,  Assistant  Chemist. 
C.  J.  Hunn,  Assistant  Horticulturist. 
V.  S.  Holt,  Assistant  in  Horticulture. 
C.  A.  Sahr,  Assistant  in  Agronomy. 

F.  A.  Clowes,  Superintendent  Hawaii  Substations. 
W.  A.  Anderson,  Superintendent  Rubber  Substation. 
J.  de  C.  Jerves,  Superintendent  Homestead  Substation. 
Joseph  K.  Clark,  Superintendent  Waipio  Substation. 
George  Copp,  Superintendent  Kula  Substation. 

(2) 


ADDITIONAL  COPIES  of  this  publication 
-TA  may  be  procured  from  the  Superintend- 
ent of  Documents,  Government  Printing 
Office,  Washington,  D.  C,  at  10  cents  per  copy 


LETTER  OF  TRANSMITTAL. 


Honolulu,  Hawaii,  August  15,  WIS. 
Sir:  I  have  the  honor  to  submit  herewith  and  recommend  for 
publication,  as  Bulletin  30  of  the  Hawaii  Agricultural  Experi- 
ment Station,  a  paper  dealing  with  the  Effect  of  Heat  on  Hawaiian 
Soils,  by  W.  P.  Kelley,  chemist,  and  William  McGeorge,  assistant 
chemist  of  the  station.  The  effect  of  heat  upon  Hawaiian  soils, 
including  highly  manganiferous  soils,  has  been  found  to  be  decidedly 
beneficial  to  the  growth  of  all  kinds  of  plants.  The  careful  study 
of  the  various  chemical  and  mechanical  changes  produced  in  soils 
by  the  application  of  heat,  as  set  forth  in  this  bulletin,  throws  con- 
siderable light  upon  the  reasons  for  this  beneficial  effect.  Studies 
on  the  effects  of  heat  on  soils  have  usually  been  confined  to  a  few 
plant-food  elements,  whereas  in  this  bulletin  a  large  number  of  the 
inorganic  and  organic  substances  are  considered.  The  bulletin  is, 
therefore,  considered  a  distinct  contribution  to  the  literature  of  this 
interesting  phase  of  soil  work. 

Respectfully,  E.  V.  Wilcox, 

Special  Agent  in  Charge. 
Dr.  A.  C.  True, 

Director  Office  of  Experiment  Stations, 

U.  S.  Department  of  Agriculture,  Washington,  D.  C. 

Publication  recommended. 
A.  C.  True,  Director, 

Publication  authorized. 
D.  F.  Houston, 

Secretary  of  Agriculture . 
(3) 


CONTENTS. 


Page. 

Introduction 5 

The  effects  of  heat  on  the  solubility  of  inorganic  constituents 7 

Preliminary  work 9 

Method  of  preparing  extracts 11 

Soil  types 12 

Silica 13 

Alumina 14 

Iron 15 

Manganese 16 

Lime  and  magnesia 18 

Potash 20 

Phosphoric  acid 21 

Sulphates 22 

Bicarbonates 23 

Effect  of  heat  upon  rice  and  taro  soils 24 

Discussion 25 

The  effects  of  heat  on  soil  nitrogen 28 

Introduction 28 

Effects  of  heat  on  nitrates 31 

Effects  of  heat  on  the  ammonia  content 32 

Effects  of  brush  burning  in  the  field 33 

Effects  of  heat  on  the  organic  nitrogen 34 

Summary 37 

(4) 


THE  EFFECT  OF  HEAT  ON  HAWAIIAN  SOILS. 


INTRODUCTION. 

Heat  as  a  means  of  stimulating  crops  has  been  made  use  of  in  cer- 
tain European  countries  for  centuries.  The  burning  of  moorlands 
and  the  paring  and  burning  of  heavy  clay  sods  were  extensively  prac- 
ticed in  times  past.  Although  their  use  at  present  is  by  no  means  as 
common  as  formerly,  these  practices  have  not  been  entirely  aban- 
doned. The  adoption  of  more  intensive  methods  of  farming,  the 
use  of  fertilizers,  cost  of  fuel,  recognition  of  the  serious  destruction 
of  the  organic  matter,  and  the  demand  for  a  more  continuous  use  of 
the  land  have  brought  about  the  gradual  disuse  of  these  ancient 
practices. 

In  America  soil  burning,  in  the  sense  it  is  understood  in  Europe, 
has  never  been  made  use  of  extensively.  In  connection  with  certain 
crops  demanding  early  forcing,  however,  soil  burning  is  practiced 
well-nigh  universally.  The  seed  of  tobacco,  cabbage  in  some  locali- 
ties, and  some  other  crops  that  are  grown  from  transplanted  seedlings 
are  still  sown  in  soil  which  has  been  previously  burned.  In  prepar- 
ing seed  beds  for  tobacco  the  soil  is  frequently  burned  heavily,  usually 
a  strong  wood  *  fire  being  maintained  on  the  bed  for  several  hours. 
It  is  a  matter  of  common  observation  that  the  growth  of  seedlings 
on  the  burned  soil  is  usually  superior  to  that  on  the  surrounding 
unburned  land.  The  effects  of  burning  are  by  no  means  confined  to 
the  germination  and  growth  of  seedlings.  In  newly  cleared  lands 
crops  of  various  kinds  usually  grow  more  rapidly  and  produce 
increased  harvests  on  the  spots  where  brush  or  log  heaps  have  been 
burned,  and  often  the  effects  persist  through  two  or  more  years. 

In  Hawaii  the  growth  of  certain  crops  is  enormously  influenced  by 
the  mere  burning  of  small  accumulations  of  brush  and  undergrowths 
of  guava  and  lantana.  The  effect  on  cotton  on  the  uplands  of  Oahu 
produced  by  these  small  fires  may  represent  the  difference  between 
success  and  failure.  The  color  and  vigor  of  the  crop  on  these  small 
areas  dotted  here  and  there  over  a  field  attract  attention.  Other 
crops  are  affected  similarly. 

1  Oil  and  gas  are  sometime;  used  for  this  purpose. 
(5) 


6 

It  has  been  known  for  a  long  time  that  burning  improves  the  struc- 
ture of  clays  by  causing  a  coalescence  of  the  smaller  particles  into 
larger  granules,  thus  effectively  improving  the  drainage.  The  in- 
creased size  of  the  pores  and  air  spaces  within  the  soil  permits  of  better 
aeration  and  encourages  deeper  root  development.  By  means  of  heat 
the  hydrous  compounds  become  dehydrated,  plasticity  and  adhe- 
siveness are  overcome,  the  movement  of  soil  moisture  facilitated,  and 
a  more  congenial  environment  for  root  development  is  produced. 
If  sufficiently  great  heat  be  employed,  the  clay  may  be  baked  into 
hard  lumps,  which  yield  to  cultural  and  weathering  influences  with 
difficulty,  and,  therefore,  injury  may  result.  In  any  event  the 
dehydrated  silicates  and  oxids  return  very  slowly  to  their  former 
state  and  the  crumb  structure  induced  by  the  heat  persists  for  years- 
The  physical  effects  of  heat  on  clays  are  so  pronounced  that  the 
admixing  of  a  few  tons  per  acre  of  the  burnt  with  the  natural  soil 
was  formerly  employed  in  Europe  as  a  means  of  ameliorating  heavy 
clay  lands. 

Regarding  the  chemical  effects  of  burning  it  is  also  well  known  that 
clay  soils  undergo  chemical  changes.  In  general  the  solubility  of 
aluminum  and  potassium  in  acids  is  greatly  increased  up  to  a  certain 
temperature,  beyond  which  a  decrease  sets  in.  It  is  generally  held 
that  under  the  influence  of  high  temperatures,  especially  with  the  aid 
of  oxidizing  conditions,  a  wasteful  destruction  of  soil  organic  matter 
and  consequent  loss  of  nitrogen  takes  place. 

In  addition  to  the  above-named  physical  and  chemical  effects  the 
killing  of  weed  seeds,  parasitic  fungi,  disease-producing  organisms, 
and  insects  are  generally  looked  upon  as  being  among  the  beneficial 
effects  of  soil  burning. 

While  the  old  system  of  burning  the  soil  has  gradually  fallen  out  of 
use,  the  closely  related  partial  sterilization  by  means  of  heat  and  vola- 
tile antiseptics  is  of  great  interest  at  the  present  time.  In  greenhouse 
work  steam  sterilization  finds  extensive  application  and  has  been  the 
subject  of  interesting  investigations  during  the  past  few  years. 
Likewise  the  action  of  dry  heat  in  its  relation  to  partial  sterilization 
and  in  comparison  with  the  effects  of  volatile  antiseptics  on  subse- 
quent biological  activities  has  received  considerable  study.  The 
old  idea  of  considering  the  subject  in  a  restricted  physical  and  limited 
chemical  sense  is,  therefore,  giving  way  to  a  broader  view  of  the 
question.  The  more  specific  chemical  effects  involved,  including  cer- 
tain physico-chemical  effects  dealt  with  more  in  detail  in  this  paper, 
and  the  biological  results  are  now  being  studied. 

It  has  been  found  that  moderate  temperatures  bring  about  an 
increase  in  the  solubility  not  only  of  the  mineral  constituents  of  soils 
but  also  in  the  organic  matter.  Furthermore,  a  number  of  investi- 
gators have  found  that  steam  sterilization,  particularly  when  under 


pressure,  frequently  produces  a  condition  that  is  toxic  both  to  the 
germination  and  the  subsequent  growth  of  plants.  Usually  the  toxic 
condition  is  of  short  duration  and  the  growth  of  crops  seems  to  aid 
effectively  in  overcoming  it.  There  are  many  phases  of  this  question 
that  are  not  fully  understood. 

There  are  two  characteristics  of  Hawaiian  soils  that  give  them 
special  interest  in  this  connection,  (1)  the  peculiarities  and  the  high 
proportion  of  the  clay;  (2)  the  inertness  of  the  unplowred  and  unbroken 
sod  lands.  The  former  gives  special  interest  to  the  question  of  heat- 
ing from  the  physical  point  of  view,  and  the  latter  is  of  interest  to  the 
question  because  of  its  bearing  on  soil  aeration.  With  but  few  excep- 
tions it  is  necessary  to  plowT  the  land,  following  with  thorough  tillage 
at  frequent  intervals  for  several  months  before  planting.  A  field 
plowed  for  the  first  time,  although  the  soil  be  thoroughly  pulverized 
and  reduced  to  a  state  of  fine  tilth,  usually  will  not  support  plant 
growth  satisfactorily.  The  farmers  of  Hawaii  have  found  it  neces- 
sary to  aerate  newly  plowed  lands  for  a  period  of  several  months 
before  planting  the  first  crop.  It  has  been  observed,  however,  that 
excellent  growth  of  crops  is  obtained  on  the  small  spots  where  brush 
was  burned  and  without  the  continued  aeration  above  referred  to. 
Heat,  therefore,  seems  to  accomplish  in  the  soil  effects  similar  to  those 
brought  about  by  aeration.  The  application  of  fertilizers  produces 
no  such  effects. 

In  connection  with  a  general  study  of  soil  aeration  the  authors 
have,  therefore,  been  led  to  a  study  of  the  effects  of  heat  on  these 
soils.  The  present  paper  deals  with  one  phase  of  this  question,  the 
physico-chemical  changes  produced.  In  the  first  part  are  presented 
the  data  obtained  with  reference  to  the  solubility  of  the  inorganic 
constituents  and  in  the  second  part  are  some  data  of  a  more  or  less 
empirical  nature  on  the  grosser  effects  of  heat  on  soil  nitrogen. 

THE  EFFECTS  OF  HEAT  ON  THE  SOLUBILITY  OF  INORGANIC 

CONSTITUENTS. 

While  a  considerable  number  of  investigators  have  studied  the 
question  of  the  effect  of  heat  upon  the  solubility  of  phosphoric  acid, 
using  various  solvents,  apparently  few  have  gone  beyond  this  and 
determined  its  effect  upon  the  solubility  of  the  remaining  mineral 
constituents  commonly  occurring  in  soils.  In  fact,  with  few  excep- 
tions, the  entire  stress  has  been  laid  upon  the  three  elements  generally 
considered  to  be  of  greatest  plant-food  value,  namely,  nitrogen,  phos- 
phoric acid,  and  potash. 

In  most  instances  the  results  of  these  earlier  investigations  have 
shown  an  increase  in  solubility  of  phosphoric  acid,  with  increase  in  the 
temperature  to  which  the  soils  have  been  heated.     M.  Xagaoka,1  on 

>  Bui.  Col.  Agr.,  Tokyo  Imp.  Univ.,  6  (1904),  No.  3,  p.  263. 


8 

igniting  soils  for  15  minutes  to  remove  humus,  found  an  increase  in 
solubility  of  phosphoric  acid,  which,  he  concluded,  was  due  to  the  de- 
struction of  organic  matter  with  which  the  phosphoric  acid  was 
combined.  He  used  as  solvents,  hydrochloric  acid,  specific  gravity 
1.15,  distilled  water,  and  several  of  the  weaker  organic  acids.  Stewart * 
used  Schmoeger's  method  of  determining  the  increase  of  solubility 
in  12  per  cent  hydrochloric  acid  before  and  after  ignition,  as  an 
indication  of  the  phosphoric  acid  combined  with  organic  matter. 
Fraps,2  while  finding  an  increase  in  the  solubility  of  phosphoric  acid 
on  ignition,  considers  that  this  increase  is  not  wholly  due  to  organic 
phosphorus,  but  that  mineral  phosphates  in  soils  are  also  rendered 
more  soluble  by  ignition,  thereby  rendering  the  ignition  method  an 
unsuitable  one  for  determining  organically  combined  phosphorus. 
On  the  other  hand,  Lipman  3  found  while  working  on  a  series  of  Cali- 
fornia soils,  that  heating  decreased  the  solubility  of  phosphoric  acid 
in  strong  nitric  acid.  Peterson  4  found  that  the  solubility  increased 
rapidly  with  increase  in  temperature  from  130°  up  to  200°  C,  but 
that  the  solubility  of  the  mineral  phosphates  in  soils  was  not  increased 
by  heating  below  240°  C. 

Valuable  work  on  the  solubility  of  the  mineral  constituents  of 
soils  is  to  be  found  among  the  publications  of  the  Bureau  of  Soils,  the 
work  being  confined  largely  to  the  use  of  water  as  solvent.  In  a 
bulletin  of  that  bureau,5  King  gives  comparative  results  of  work  upon 
fresh  and  oven-dried  soils  which  show  the  effect  of  heating  to  110°  C. 
to  be  striking.  On  the  average  more  nitrates,  phosphoric  acid,  sul- 
phates, bicarbonates,  and  silica  were  recovered  from  the  oven-dried 
soils  than  from  the  fresh  samples,  while  the  average  of  the  chlorin 
determinations  showed  a  decrease.  No  determination  of  the  basic 
constituents  are  tabulated,  but  King  states  that  upon  later  investi- 
gations he  found  an  increase  in  potash,  lime,  and  magnesia  in  oven- 
dried  soils.  He  makes  several  suggestions  as  to  the  cause  of  this  in- 
crease, both  from  a  physical  and  chemical  standpoint,  but  it  is  evident 
from  his  discussions  that  he  considered  the  cause  to  be  primarily 
physical.  A  number  of  other  investigators  have  noted  an  increase 
in  total  inorganic  matter  soluble  in  water 6  as  a  result  of  heating, 
but  no  separation  of  the  elements  was  made. 

The  special  phase  to  which  this  paper  is  devoted  is  that  of  the  effect 
of  heat  upon  the  solubility  of  the  mineral  constituents,  distilled  water 
and  fifth-normal  nitric  acid  being  used  as  solvents. 

i  Illinois  Sta.  Bui.  145. 
2  Texas  Sta.  Bui.  136. 

*  Jour.  Indus,  and  Engin.  Chem.,  4  (1912),  No.  9,  p.  663. 

*  Wisconsin  Sta.  Research  Bui.  19. 

*  U.  S.  Dept.  Agr.,  Bur.  Soils  Bui.  26,  p.  55. 
6  New  York  Cornell  Sta.  Bui.  275. 


PRELIMINARY    WORK. 

The  results  of  some  preliminary  experiments  on  three  Hawaiian 
soils  dealing  with  the  various  methods  of  preparing  soil  extracts  with 
distilled  water  are  presented  in  the  following  table: 

Influence  of  state  of  moisture  and  time  of  extraction  on  composition  of  the  water  extract 

of  soils. 
[In  parts  per  million  of  dry  soil.] 


Length 
of  ex- 
traction. 

Bicar- 

bo- 

nates 

(HC03.) 

Iron 
oxid 
and 
alu- 
mina 

(Fe203 
and 

A1203). 

Phos- 
phoric 

acid 
(P204). 

Man- 
ganese 
oxid 
(Mn3 
04). 

Lime 
(CaO). 

Mag- 
nesia 
(MgO). 

Sul- 
phuric 

acid 
(S03). 

Potash 
(K20). 

Soil  No.  313: 

Fresh 

Air  dried 

Oven  dried 

Fresh 

1  hour... 

...do 

...do 

24  hours. 

...do 

...do 

7  days... 

...do 

...do 

1  hour... 

...do 

...do 

24  hours. 

...do 

...do 

7  days... 

...do 

...do 

1  hour... 
...do 

...do 

155.0 
1, 040. 0 
358.0 
95.6 
678.0 
246.0 
191.0 
562.0 
262.0 

97.8 
708.0 
371.0 
117.7 
651.  0 
228.0 
157.0 
688.0 
180.0 

140.0 
975.  0 
558.0 
200.0 

53.5 

8.7 
12.8 
17.8 
13.0 
19.2 
45.8 
44.5 
49.1 

38.6 
4.3 

2.03 
1.95 
2.35 
2.55 
1.74 
3.42 
2.55 
.    2.38 
3.00 

2.32 
1.94 

2.55 

17.4 

"2.  55* 
15.20 

"i5.'2" 
88.9 

2.5 
27.4 

122.2 

121.8 
197.0 
148.0 

86.8 
120.0 

96.9 
160.  5 
102.2 

56.  5 
77.2 
89.0 
77.0 
43.0 
85.0 
71.9 
47.2 
63.8 

127.6 
224.0 
194.1 
197.6 
103.2 
123.5 
206. 7 
162.0 
212.0 

62.7 
103. 0 
159.0 

77.6 
102.0 
126.2 

68.3 
168.0 
116.0 

14.8 
105. 2 
99.8 
39.0 
88.5 
113.5 
70.4 
76.1 
109.0 

60.2 
120.0 
119.5 
105.1 

81.5 
103.5 

55.0 
102.0 
124.0 

247.0 
120.0 
194.0 
257.2 
134.5 
199.0 
221.5 
171.0 
145.0 

114.0 
81.0 
145. 0 
175.6 
72.0 
131.0 
137.1 
83.8 
151.0 

137.1 
105.  5 
136.0 
133.  7 

67.2 
133.0 
155.  6 

£3. 1 
159.0 

133.0 
256.0 
143.0 
226.6 

Air  dried 

Oven  dried 

Fresh 

213.0 
121.0 
239.8 

Air  dried 

Oven  dried 

Subsoil  No.  314: 

Fresh 

282.0 
61.0 

150.  5 

Air  dried 

Oven  dried 

142.0 
64.1 

Fresh 

43.7 
10.8 
14.8 
23.2 
6.4 
17.0 

3.04 
20.2 
11.2 

4.6 
40.5 
15.4 
10.3 

9.0 

2.32 
2.14 
2.96 
2.05 
2.14 
2.76 

.76 
1.80 
7.05 
1.37 
1.80 
3.31 
1.06 
2.02 

5.1 
30.1 

"u.s" 

17.2 

1.52 
15.70 

'"4."6" 
15.7 

""7.'6" 
29.2 

208.5 

Air  dried 

Oven  dried 

Fresh 

181.0 
118.0 
227.0 

Air  dried 

Oven  dried 

Soil  No.  319: 

Fresh 

158. 2 
68.0 

142.2 

Air  dried 

Oven  dried 

Fresh 

278.0 
135.0 
170.8 

Air  dried 

Oven  dried 

p'resh 

...do 1,300.0 

...do 270.0 

7  days...!      99.0 

...do 1,280.0 

...do 485.0 

274.0 
70.5 
155.0 

Air  dried 

Oven  dried 

234.0 
147.0 

The  soils  chosen  were  from  the  Koolaupoko  district,  on  Oahu, 
No.  313  being  a  sample  of  brown  ferruginous  clay  soil  which  occurs 
widely  distributed  in  this  district.  It  was  very  dry  at  the  time  of  sam- 
pling and  was  covered  with  a  heavy  growth  of  guava.  No.  314  is  the 
subsoil  to  No.  313,  and  No.  319  is  a  sample  of  a  similar  type  which 
had  been  plowed  and  planted  to  pineapples. 

The  extracts  were  made  by  treating  the  soils  with  distilled  water 
in  the  proportion  of  5  parts  of  the  latter  to  1  of  the  former  in  glass- 
stoppered  bottles,  shaking  occasionally  during  the  period  noted  in 
the  table,  each  being  shaken  an  equal  number  of  times.  The  values 
are  figured  to  parts  per  million  of  the  oven-dry  soil.  Sample  No.  313 
contained,  originally,  18.65  per  cent  moisture,  No.  314  19.65  per  cent, 
and  No.  319  30.3  per  cent. 

It  will  be  seen  that  in  every  case  the  air-dried  soil  contained  the 
largest  amount  of  soluble  HC03,  the  oven-dried  sample  next,  and  the 
fresh  soil  the  least,  regardless  of  the  time  of  extraction. 
14060°— Bull.  30—13 2 


10 

No  attempt  was  made  to  separate  iron  oxid  and  alumina,  but  the  de- 
termination seems  to  vary  considerably  in  the  different  soils.  No.  313 
apparently  increased  in  solubility  with  increase  in  time  of  extraction. 
If  the  abnormal  figure,  53.5,  be  disregarded,  the  difference  between  the 
fresh,  air-dried,  and  oven-dried  soil  is  very  slight.  In  the  subsoil  air 
drying  produced  a  decrease  in  solubility,  but  the  oven-dried  were 
more  soluble  than  the  air-dried  samples.  The  results  from  No.  319 
are  discordant,  but  indicate  the  air-dried  form  to  be  the  most  soluble. 

Phosphoric  acid. — This  series  is  remarkably  concordant  and  indi- 
cates an  increase  in  solubility  of  this  constituent  upon  drying  in  the 
oven  and  at  the  same  time,  without  exception,  shows  an  increase  in 
solubility  with  increase  in  time  of  extraction. 

Manganese. — These  results  indicate  an  increase  in  solubility  of 
manganese  with  increase  in  time  of  extraction  and  also  an  increase  in 
solubility  upon  drying.  Unfortunately  the  whole  series  of  manganese 
determinations  on  the  oven-dried  samples  was  lost  through  accident. 

Lime. — While  the  results  from  the  lime  determinations  are  very 
inconsistent,  the  general  average  tends  to  show  an  increase  in  solu- 
bility upon  heating  in  the  oven  and  a  maximum  solubility  in  the  one- 
hour  period  of  extraction.  This  latter  may  be  due,  however,  to  sub- 
sequent precipitation  in  the  longer  extractions. 

Magnesia. — The  table  shows  a  marked  consistency,  especially  with 
reference  to  the  rate  of  increase  in  solubility  of  magnesia,  due  to 
drying.  The  concentration  of  the  extracts  from  the  fresh  soils  was 
least,  with  only  one  exception,  while  that  from  the  oven-dried  soils 
was  greatest  in  most  instances.  While  there  is  considerable  varia- 
tion, the  data  indicate  the  most  complete  extraction  in  that  of  seven 
days'  duration. 

Sulphuric  acid. — The  relative  amounts  of  this  constituent  extracted 
show  it  to  be  slightly  more  soluble  in  the  fresh  soil,  judging  from  the 
average  of  the  series,  although  only  slightly  more  so  than  in  the 
oven-dried  soil,  and  that  the  concentration  is  practically  the  same 
for  the  several  periods  of  extraction. 

Potash. — The  potash  series  shows  this  element  to  be  much  more 
soluble  in  the  air-dry  and  fresh  soils  than  in  the  oven-dried  soils, 
while  there  is  scarcely  any  difference  in  the  solubility  as  induced  by 
increasing  the  time  of  extraction  from  24  hours  to  7  days. 

The  above  results  tended  to  establish  the  advisability  of  an  arbi- 
trary extraction  of  not  over  24  hours,  and  partly  for  this  reason  it  was 
decided  that  the  method  at  present  in  general  use,  namely,  shaking 
for  a  period  of  1  hour  and  allowing  to  settle  for  24  hours  would  be 
suitable  to  our  conditions.  Owing  to  the  mechanical  texture  of 
Hawaiian  soils,  caused  by  the  presence  in  them  of  highly  ferruginous 
clays,  which  assume  a  colloidal  form  if  worked  when  too  wet,  it  was 
found  necessary  to  allow  the  extracts  to  settle  and  in  every  instance, 
except  when  heated  to  250°  C.  or  ignited,  it  was  necessary  to  add  a 


11 

coagulant.  Not  having  the  apparatus  to  effect  a  rapid  filtration 
through  clay  filters,  small  amounts  of  ammonium  chlorid  were  used 
to  bring  about  coagulation  of  the  clay  and  make  filtration  through 
filter  paper  possible.  In  addition  to  using  distilled  water  as  a  solvent, 
fifth-normal  nitric  acid  was  chosen  in  order  to  gain  additional  infor- 
mation concerning  the  action  of  different  solvents.  The  means 
chosen  for  drying  the  soils  were  in  an  air  bath  at  100°  C,  and  250°  C, 
over  a  Bunsen  burner.  It  being  practically  impossible  to  obtain 
ignition  all  the  samples  fresh,  extraction  upon  the  soils  in  this  state 
was  not  attempted. 

METHOD   OF   PREPARING   EXTRACTS. 

The  soils  were  prepared  as  follows:  Upon  receipt  in  the  labora- 
tory they  were  spread  out  to  dry.  After  reaching  an  approximately 
stable  moisture  content  portions  were  weighed  into  porcelain  dishes. 
One  series  was  dried  in  an  oven  at  100°  C.  for  8  hours  continuously, 
another  treated  likewise  at  250°  C,  while  the  last  series  was  heated 
over  a  Bunsen  burner,  at  first  carefully  on  a  wire  gauze  for  2  hours  to 
prevent  dusting  and  then  over  the  direct  flame  for  2  hours,  thus 
destroying  practically  all  the  organic  matter. 

Water  extract. — This  extraction  was  made  by  treating  200  gram 
portions  of  the  soils  with  1  liter  distilled  water,  shaking  occasionally 
for  1  hour,  as  previously  mentioned,  and  then  allowing  to  settle  24 
hours,  adding  small  amounts  of  ammonium  chlorid  as  a  coagulant 
when  necessary.  Particular  attention  was  given  to  these  extrac- 
tions in  order  that  all  the  samples  in  each  series  of  the  same  soil 
should  receive  similar  treatment  as  regards  the  number  of  times  of 
shaking,  thus  making  the  results  more  directly  comparable.  Like- 
wise, all  distilled  water  for  a  series  was  taken  from  the  same  lot  in 
order  to  eliminate  any  slight  influence  which  varying  amounts  of  car- 
bon dioxid  in  the  distilled  water  would  have  upon  the  solubility  of 
the  minerals.  After  settling  24  hours  the  solution  was  filtered 
through  double  filter  papers  and  from  this  solution  500  cubic  centi- 
meters was  evaporated  to  a  small  volume  and  used  for  analysis. 
All  determinations  were  made  gravimetrically  except  phosphoric 
acid,  iron,  and  bicarbonate.  The  former  was  made  colorimetrically 
in  50  cubic  centimeters  of  the  original  solution.1  Iron  was  deter- 
mined colorimetrically 2  in  a  solution  of  the  ammonia  precipitate 
from  the  500  cubic  centimeters  portion,  and  bicarbonate  was  de- 
termined by  titrating  50  cubic  centimeters  of  the  original  solution 
with  twentieth-normal  acid  potassium  sulphate,  using  methyl  orange 
as  indicator. 

Nitric  acid  extract. — The  soils  for  this  phase  of  the  work  were  pre- 
pared in  the  same  manner  as  above  described  as  regards  tempera- 

'U.  S.  Dept.  Agr.,  Bur.  Soils  Bui.  31,  p.  45. 
«U.  S.  Dept.  Agr.,  Bur.  Soils  Bui.  31,  p.  38. 


12 


tures  and  time  of  heating.  However,  in  this  work  only  100  grams 
were  treated  with  500  cubic  centimeters  fifth-normal  nitric  acid.  The 
extraction  differed  in  that  the  soils  were  shaken  occasionally,  for  a 
period  of  5  hours,  and  then  filtered  directly  through  double  filter 
papers.  All  determinations  were  made  gravimetrically  in  100  cubic 
centimeters  of  this  filtrate  with  the  exceptions  of  iron,  which  was 
determined  volumetrically,  and  phosphoric  acid  and  titanium,  which 
were  determined  colorimetrically  in  25  cubic  centimeter  portions  of 
the  original  extract. 

SOIL   TYPES. 

The  types  of  soil  selected  for  this  work  were  of  the  widest  possi- 
ble range,  and  represented,  in  a  general  way,  the  normal  and  ab- 
normal types,  both  physical  and  chemical,  to  be  found  in  the  islands. 
The  following  table  gives  the  chemical  analyses  of  samples  as  deter- 
mined with  hydrochloric  acid  of  specific  gravity  1.115: 
Chemical  analyses  of  soils  used. 


Soil 
No. 

74. 


Soil 
No. 
164. 


Soil 
No. 


Soil 
No. 
292. 


SoU 
No. 
290. 


Soil 
No. 
405. 


Soil 
No. 
416. 


Soil 
No. 
417. 


Soil 
No. 
406. 


Soil 
No. 

428. 


Soil 
No. 
426. 


Soil 
No. 
448. 


Moisture  (H20) 

Volatile  matter 

Insoluble  matter 

Iron  oxid  (Fe203) 

Alumina  (AI2O3) 

Titanium  oxid  (Ti02) 

Manganese  oxid  (Mn304) . . . 

Lime(CaO) 

Magnesia  (MgO) 

Potash  (K20) 

Soda(Na20) 

Sulphuric  acid  (SO3) 

Phosphoric  acid  (P2Os) 


P.ct 

25.46 
13.08 
32.69 
10.13 
12.59 


.13 

2.63 

1.09 

.14 

.34 

.22 

1.02 


P.ct 
1.22 
3.56 

48.17 
30.58 

3.05 

1.72 
.10 
.12 

1.22 
.48 

1.46 
.44 
.08 


P.ct 

5.36 

16.78 

31.67 

18.60 

14.67 

.68 

9.21 

1.32 

.52 

.79 

.38 

.15 

.20 


P.ct. 

7.65 

8.42 

38.49 

16.63 

12.85 

2.00 

.24 

1.84 

8.71 

.39 

1.36 

.08 

.57 


P.ct. 

8.44 

15.80 

40.02 

16.41 

14.11 

1.50 

.30 

.77 

1.30 

.17 

.42 

.10 

.27 


P.ct 

8.02 

12.50 

39.12 

15.24 

20.54 

2.40 

.15 

.86 

.99 

.20 

.48 

.33 

.44 


P.ct. 

6.17 

17.73 

36.09 

13.20 

20.39 

1.60 

3.84 

.33 

.44 

.39 

.59 

.35 

.20 


P.ct. 

16.26 

17.53 

30.92 

11.24 

19.38 

1.40 

2.85 

.21 

.36 

.45 

.36 

.43 


P.ct. 

10.34 

17.73 

37.31 

10.92 

20.20 

1.80 

.06 

.48 

.67 

.20 

.48 

.30 

.48 


P.ct 

14.94 

22.24 

34.99 

8.24 

10.73 

3.20 

.20 

1.91 

2.24 

.24 

1.40 

.45 

.22 


P.ct 

10.47 

18.28 

24.80 

22.52 

19.10 

3.80 

.22 

.15 

.44 

.28 

.74 

.39 

.19 


P.ct. 

16.00 

25.58 

15.10 

19.20 

16.64 

4.20 

.06 

.50 


No.  74  is  a  yellowish-brown  soil  from  Waimea,  Hawaii,  of  sandy 
silt  texture,  with  an  abnormally  low  clay  content,  and  maintains  a 
very  loose,  open  structure. 

No.  16T4  represents  a  peculiar  type  of  soil  more  or  less  scattered 
over  the  islands,  which  upon  absolute  analysis  shows  about  20  per 
cent  of  titanium  oxid.  It  is  high  in  iron  and  aluminum,  and  also 
contains  a  larger  percentage  of  ferrous  iron  than  any  of  the  soils 
examined  heretofore.  It  has  a  high  specific  gravity,  bluish-gray 
color,  packs  quite  closely,  has  a  " clayey  silt"  texture,  and  contains 
an  abnormally  low  content  of  moisture  and  organic  matter. 

No.  9  is  a  sample  of  the  highly  manganiferous  type  found  in  the 
Wahiawa  district  on  Oahu.  It  has  a  chocolate-brown  color,  a  sandy 
silt  texture,  and  maintains  an  excellent  mechanical  condition,  thus 
permitting  good  aeration. 

No.  292  represents  the  type  of  soil  occurring  in  the  lowlands  in 
and  about  Honolulu  now  being  used  for  bananas,  rice,  and  truck 
farming.  It  has  a  sandy  texture,  grayish-brown  color,  and  abnor- 
mally high  magnesia  content. 


13 


No.  290  is  a  peculiar  type  of  soil  occurring  in  the  valley  on  the 
experiment  station  grounds,  and  is  undoubtedly  of  sedimentary 
origin,  its  nature  being  largely  determined  by  washings  from  the 
mountain.  It  is  a  blue  clay  soil,  exceedingly  plastic  when  wet,  but 
upon  drying  forms  hard  compact  lumps,  and  is  somewhat  similar  to 
adobe  or  gumbo  soils.  This  soil  also  has  a  soapy  feel,  and  during 
the  rainy  season  aeration  and  drainage  are  almost  impossible. 

Nos.  405  and  406  are  samples  of  a  silty  soil,  to  be  found  in  the 
Kalihi  district  of  Honolulu,  which  is  being  used  for  aquatic  agricul- 
ture, the  former  for  rice,  the  latter  for  taro  culture. 

Nos.  416  and  417  represent  the  type  of  red  clay  soil  which  is  so 
abundant  on  all  the  islands.  These  samples  were  taken  only  a  short 
distance  apart  with  the  view  in  mind  of  determining  the  effect  of 
cultivation,  416  being  a  cultivated  soil,  while  417  is  practically  the 
same  soil  from  the  unbroken  sod. 

Xo.  428  is  a  sample  of  highly  organic,  dark-colored  soil  from  Glen- 
wood,  Olaa  district,  Hawaii.  It  has  a  very  sandy  texture  and  is 
subjected  to  heavy  rainfall  and  good  drainage,  but  for  some  reason, 
probably  climatic,  is  unproductive. 

No.  426  is  a  sample  from  Kealia,  Kauai,  and  represents  a  brown 
type  of  soil  which  has  partly  undergone  a  recementation  of  the  par- 
ticles into  a  yellow  soft  rock,  hence  the  sample  contains  considerable 
gravel. 

No.  448  represents  the  type  of  yellow  clay  scattered  throughout 
the  islands  in  certain  districts,  this  sample  having  been  taken  from 
near  Hilo,  Hawaii. 

The  relative  solubility  of  the  various  constituents  is  shown  sepa- 
rately in  order  to  bring  out  more  clearly  the  effects  of  heat,  one  table 
being  devoted  to  each  element. 

silica. 

The  following  table  shows  the  results  obtained  in  the  study  of  the 
effect  of  heating  on  the  solubility  of  the  silica: 

Solubility  of  silica  in  water  and  fifth-normal  nitric  acid. 
[Calculated  on  basis  of  dry  soil.i 


Soluble  in  water  (parts  per  million). 

Soluble  in  fifth-normal  nitric  acid  (per 
cent;. 

Soil  No. 

Air  dry. 

Dried  at 
100°  c. 

Dried  at 
250°  C 

Ignited. 

Air  dry. 

Dried  at 
100°  c. 

Dried  at 
250°  C 

Ignited. 

74 

35.3 
10.0 

4.2 
2.2 
2.3 

12.5 
2.4 
4.0 

15.9 
1.15 
0.0 

13.0 
2.0 
9.5 
8.3 
2.1 
6.9 
7.8 

10.5 
4.5 

14.9 
3.38 
0.0 

8.7 
3.0 
8.5 
7.2 

17.2 
5.7 
7.8 
9.4 

31.2 
8.9 
7.9 
0.0 

8.7 

4.0 

7.  1 

10.3 

8.6 

16.1 

10.4 

22.3 

33.5 

11.9 

1.13 

8.0 

0. 196 
.007 
. .  15 
.102 
.  150 
.180 
.  005 
.070 
.165 
.289 
.024 
.211 

0.187 
.006 
.091 
.680 
.148 
.219 
.055 
.076 
.173 
.261 
.009 
.226 

0.113 
.027 
.084 

.616 
.264 
.240 
.077 
.097 
.301 
.202 
.062 
.077 

0.225 

164 

.067 

9 

.190 

292 

.523 

290 

.596 

405 

.267 

416 

.192 

417 

206 

ttfl 

428 

426 

.292 
.  320 
.158 
.327 

14 

The  results  of  the  silica  determinations  in  the  water  extract  are 
rather  inconsistent,  but  the  average  shows  the  highest  solubility  at 
ignition.  It  will  be  observed  that  the  data  obtained  with  fifth-normal 
nitric  acid  disclose  some  very  interesting  facts  which  show  that  an 
increase  in  solubility  of  silica  in  dilute  nitric  acid  in  Hawaiian  soils 
is  produced  upon  heating  to  ignition.  Furthermore,  the  tendency 
points  toward  a  general  increase  in  solubility  with  increase  in  tempera- 
ture. Attention  is  called  to  the  fact  that  the  soils  high  in  magnesia 
show  the  greatest  solubility  of  silica  in  dilute  nitric  acid.  An  excep- 
tion in  this  particular  is  found  in  sample  No.  164,  a  soil  almost  devoid 
of  organic  matter  and  containing  a  very  high  titanium,  iron,  and 
silica  content.  A  further  discussion  of  these  results  will  be  taken  up 
following  the  table  of  alumina  determinations  in  consideration  of  the 
relation  of  these  two  elements  in  the  soil. 

ALUMINA. 

The  following  table  shows  the  results  obtained  in  the  determinations 
of  alumina  in  heated  and  unheated  soils: 

Solubility  of  alumina  in  water  and  fifth-normal  nitric  acid. 
[Calculated  on  basis  of  dry  soil.] 


' 

Soluble  in  water  (parts  per  million). 

Soluble  in  fifth  normal  nitric  acid  (per 
cent). 

Soil  No. 

Air  dry. 

Dried  at 
100°  c. 

Dried  at 
250°  C 

Ignited. 

Air  dry. 

Dried  at 
100°  C. 

Dried  at 
250°  C 

Ignited. 

74 

11.1 

7.5 

4.8 

16.6 

19.1 

7.6 

17.6 

15.3 

10.3 

4.4 

2.9 

4.9 

3.2 

9.5 

1.1 

17.6 

12.7 

13.8 

12.8 

9.0 

19.6 

6.3 

6.6 

.7 

10.3 

9.5 

9.5 

14.5 

12.8 

17.6 

16.1 

4.8 

28.5 

11.9 

1.7 

5.8 

22.3 

5.0 

3.7 

17.1 

17.7 

12.2 

20.9 

28.9 

38.0 

8.8 

2.1 

2.6 

0.291 
.060 
.583 
.874 
.266 
.169 
.420 
.679 
.295 

2.261 
.308 
.979 

0.292 
.048 
.675 
.598 
.292 
.133 
.509 
.661 
.314 

2.031 
.347 

1.757 

0.318 

.139 

.676 

.584 

.691 

.444 

1.057 

1.413 

.882 

2.208 

1.192 

1.966 

0.9.56 

164... 

.288 

9 

1.034 

292 

1.055 

290...              

.749 

405 

.897 

416 

1.515 

417 

1.495 

406 

1.425 

428 

2.244 

426 

1.571 

448 

2.757 

It  will  be  observed  from  this  table  that  the  alumina  is  affected  in 
very  much  the  same  way  as  the  silica.  The  results,  while  somewhat 
inconsistent,  show  an  increase  in  water-soluble  alumina  in  the  heated 
soils,  the  number  showing  increase  of  alumina  by  heating  from  100  to 
250°  C,  being  about  the  same  as  in  passing  to  ignition.  The  effect  of 
heat  upon  the  solubility  of  this  element  in  dilute  nitric  acid  is  very 
marked  and  increases  regularly  with  increase  in  temperature.  There 
is  scarcely  any  correlation  between  the  solubility  of  the  alumina  and 
the  total  amount  of  silica  present.  However,  it  is  worthy  of  note 
that  there  seems  to  be  a  relation  between  the  solubility  of  the  alumina 
in  dilute  nitric  acid  and  the  volatile  matter  (organic  matter  and 
combined  water)  existing  in  the  soil,  as  will  be  readily  seen  from  the 


15 

table.  Soil  No.  164  is  almost  devoid  of  organic  matter  and  combined 
water  and  contains  the  least  soluble  alumina,  while,  on  the  other 
hand,  those  soils  in  which  the  volatile  matter  is  highest  contain  the 
most  soluble  alumina,  this  being  especially  noticeable  in  soils  Nos. 
428  and  448. 

The  effect  of  heat  upon  the  solubility  of  alumina  and  silica, 
especially  in  water,  is  probably  referable  to  a  number  of  causes.  It 
is  believed,  however,  to  be  primarily  physical,  being  related  to  an 
alteration  of  the  films  surrounding  the  soil  particles  and  to  a  modifica- 
tion of  the  colloidal  forms  which  these  elements  probably  assume 
under  the  prevailing  conditions.  The  former  effect  will  be  discussed 
in  greater  detail  farther  on.  Dehydration  and  certain  chemical 
alterations  at  the  higher  temperatures  would,  on  the  other  hand, 
tend  toward  increasing  the  solubility  in  acids  through  the  action  of 
heat  upon  the  hydrated  silicates.  It  has  long  been  known  that 
certain  aluminum  silicates  become  more  soluble  in  acids  as  a  direct 
effect  of  heat.  In  the  early  manufacture  of  alum  advantage  was 
taken  of  this  fact. 

IRON. 


The  relative  amounts  of  iron  (Fe203)  recovered  by  the  two  solvents 
appear  in  the  following  table: 

Solubility  of  iron  in  water  and  fifth-normal  nitric  acid. 
[Calculated  on  basis  of  dry  soil.] 


Soil  No. 

Soluble  in  water  (parts  per  million). 

Soluble  in  fifth-normal  nitric  acid  (per 
cent). 

Air  dry. 

Dried  at 
100°  c. 

Dried  at 
250°  C 

Ignited. 

Air  dry. 

Dried  at 
100°  c. 

Dried  at 
250°  C. 

Ignited. 

74 

17.6 
3.5 
3.7 
2.9 
4.8 
6.4 
2.8 
5.2 
4.6 
1.9 
1.7 
2.1 

9.7 
3.5 
5.3 
5.3 
3.2 
9.2 
2.8 
2.7 
2.7 
2.7 
1.3 
3.2 

9.2 
3.5 
3.9 
3.1 
4.4 
5.4 
2.8 
3.3 
4.0 
3.2 
1.6 
2.3 

12.5 
5.1 
4.5 
3.5 
1.8 
5.1 
2.5 
3.8 
2.1 
1.6 
1.3 
2.1 

0.003 
.005 
.007 
.194 
.069 
.324 
.032 
.026 
.515 
.024 
.037 
.051 

0.002 
.007 
.016 
.037 
.069 
.302 
.032 
.029 
.487 
.  033 
.061 
.038 

0.006 
.083 
.006 
.037 
.142 
.290 
.027 
.029 
.333 
.039 
.014 
.077 

0.055 

164 

.047 

9 

.006 

292 

.013 

290 

.046 

405 

.157 

416 

.015 

417 

.033 

406 

.158 

428 

.107 

426.... 

.082 

448 

.024 

Again,  there  is  considerable  inconsistency  in  the  results,  but  an 
average  shows  the  solubility  of  iron  in  water  to  be  greatest  in  the 
air-dried  soil.  The  solubility  in  dilute  nitric  acid  is  much  less  con- 
sistent than  that  in  water,  thereby  making  it  impossible  to  advance 
any  conclusions  except  to  call  attention  to  the  fact  that  the  alumina 
in  Hawaiian  soils  is  very  much  more  soluble,  both  in  water  and  in 
dilute  nitric  acid,  than  is  the  iron.  But  if  the  results  from  samples 
Xos.  292,  405,  and  406  be  disregarded,  and  this  is  plainly  permissible 
since  these  soils  are  used  in  aquatic  agriculture  and  the  major  part 
of  the  soluble  iron  is  in  the  ferrous  condition  and  would  be  oxidized 


16 


to  the  ferric  condition  on  being  heated  to  higher  temperatures,  thus 
becoming  less  soluble,  then  the  figures  show  a  marked  increase  in 
solubility  of  the  iron  with  increase  in  temperature.  It  will  be  noticed 
that  the  three  soils  which  it  is  proposed  to  disregard  in  drawing  con- 
clusions show  a  markedly  regular  decrease  in  solubility  of  the  iron 
from  the  air-dried  to  the  ignition  state.  A  qualitative  test  of  the 
water  extract  from  these  three  soils  showed  a  very  high  concentra- 
tion of  ferrous  iron  from  the  wet  and  air-dry  samples.  In  several  of 
the  samples  in  the  series  there  is  a  close  correlation  between  the  effects 
of  the  heat  on  iron  and  alumina,  but  it  is  by  no  means  general. 

Iron,  alumina,  and  silica  are  apparently  the  constituents  least  solu- 
ble in  water.  The  greater  solubility  of  iron  in  the  air-dried  soil  may 
be  explained  by  the  fact  that  the  normal  mechanical  condition  of 
Hawaiian  soils  is  conducive  to  reducing  conditions  which  result  in 
the  formation  of  small  quantities  of  ferrous  compounds.  Hawaiian 
soils,  although  characteristically  basic,  normally  give  an  acid  reac- 
tion, due  indirectly  to  the  high  clay  content  and  its  accompanying 
poor  aeration.  Magnification  of  this  condition  is  to  be  found  in  the 
rice  and  taro  soils,  as  will  be  shown  in  a  later  table  (p.  24),  in  which 
soluble  iron  is  found  in  comparatively  large  amounts.  In  such  cases 
it  is  to  be  expected  that  the  direct  effect  of  heat  would  be  to  oxidize 
the  iron  and  thus  render  it  less  soluble.  Further  confirmation  of 
this  theory  is  found  in  the  cultivated  and  uncultivated  soils  (Nos. 
416  and  417,  respectively),  in  which  the  iron  content  of  the  latter  is 
shown  to  be  the  more  soluble.  After  heating  at  100°  the  solubility 
in  many  instances  is  greater  than  in  the  air-dry  samples  and  is  prob- 
ably due  to  physico-chemical  effects  upon  the  soil  films  and  hydrated 
silicates.  These  latter  effects  are  also  responsible  for  the  increased 
solubility  of  iron  in  dilute  nitric  acid  as  a  result  of  heat. 

MANGANESE. 

The  results  obtained  from  the  manganese  (Mn304)  determinations 
are  shown  in  the  following  table : 

Solubility  of  manganese  in  water  and  fifth-normal  nitric  acid. 
[Calculated  on  basis  of  dry  soil.] 


Soluble  in  water  (parts  per 

million). 

Soluble  in  fifth-normal  nitric 
cent). 

acid  (per 

Soil  No. 

Air  dry. 

Dried  at 
100°  C. 

Dried  at 
250°  C. 

Ignited. 

Air  dry. 

Dried  at 
100°  C. 

Dried  at 
250°  C. 

Ignited. 

74 

26.5 
9.0 

23.5 
5.2 

29.4 
5.9 
2.2 

15.  7 
9.1 

l.i.  9 
6.9 
2.8 

30.4 
11.0 

26.5 

4.1 
20.4 
10.3 

4.5 
£8.7 

4.4 
161.1 

9.0 
13.4 

30.4 
10.0 
25.5 
41.4 
40.8 
14.9 
14.4 

180.5 

6.0 

32.8 

90.3 

108.7 

30.4 

9.0 

20.1 

14.5 

45.1 

18.4 

14.8 

219.2 

9.6 

6.3 

33.8 

119.6 

0.063 
.003 
.494 
.070 
.049 
.062 
.349 
.385 
.035 
.094 
.004 
.028 

0.041 
.008 
.  669 
.098 
.076 
.062 
.529 
.580 
.030 
.102 
.012 
.032 

0.217 
.013 

1.692 
.106 
.115 
.047 

1.314 

1.052 
.048 
.225 
040 
.126 

0.071 

1C4 

.006 

9 

1. 129 

292 

.067 

290 

.118 

405 

.041 

416  

.739 

417 

.748 

406 

.040 

428 

.135 

426 

.023 

448           

.050 

17 

'  This  table  shows  that  the  solubility  .of  manganese  in  water  is  much 
greater  in  the  heated  soils/being  most  soluble  in  the  ignited  samples. 
The  surprising  feature  of  this  table  is  the  fact  that  several  of  the  soils 
in  the  series  show  manganese  in- a  much  more  soluble  form  than  the 
manganiferous  soil  containing  9.21  per  cent  total  Mn304.  A  possible 
explanation  is  found  in  the  results  upon  the  cultivated  and  unculti- 
vated soils  (Nos.  416  and  417,  respectively),  namely,  that  cultivation 
and  the  accompanying  aeration  has  the  effect  of  producing  a  lower 
state  of  oxidation  or  other  changes  which  render  the  manganese  less 
soluble  in  water.  An  observation  of  Nos.  416  and  417  (cultivated  and 
uncultivated)  shows  a  large  decrease  in  solubility  as  a  result  of  culti- 
vation, and  the  highly  manganiferous  soil  (No.  9)  has  been  in  culti- 
vation for  some  time.  - 

The  table  showing  the  solubility  of  manganese  in  dilute  nitric  acid 
presents  a  remarkably  consistent  series  of  results,  as  is  shown  by  the 
increase  in  solubility  as  a  result  of  the  action  of  heat  up  to  250°  C, 
followed  by  a  large  decrease  as  effected  by  ignition.  This  is  true  with 
only  two  exceptions  in  the  entire  series. 

It  is  difficult  to  explain  the  effects  of  heat  upon  the  solubility  of 
manganese.  This  element  occurs  in  some  Hawaiian  soils  as  concre- 
tions, especially  in  the  highly  manganiferous  soils,  and  is  present,  at 
least  partially,  as  manganese  dioxid.  But  in  the  normal  types  con- 
cretions are  absent,  and  here  the  manganese  probably  exists  largely 
in  a  lower  state  of  oxidation,  and  hence  in  a  more  soluble  form.  In 
any  case  manganites  and  salts  may  occur  to  a  limited  extent.  As 
already  noted,  the  soils  heated  to  250°  C.  and  ignition  gave  the  more 
concentrated  water  extract,  an  average  indicating  the  maximum  con- 
centration from  the  ignited  soils.  The  effect  of  heat  upon  the  phys- 
ical properties  is  probably  the  prime  factor  which  influences  the  sol- 
ubility in  water.  With  one  exception  the  oxids  of  manganese  are 
quite  insoluble  in  nitric  acid,  this  oxid  being  manganous  oxid  (MnO). 
Therefore  the  higher  oxids,  such  as  manganomanganic  oxid  (Mn304) 
and  manganic  oxid  (Mn203) ,  which  are  both  essentially  combinations 
of  manganese  dioxid  and  manganous  oxid,1,  are  soluble  in. nitric  acid 
to  the  extent  of  their  MnO  content,  while  their  Mn02  content  remains 
insoluble.  Consequently  the  solubility  of  manganese  oxids  increases 
with  increase  in  heat  owing  to  the  above-mentioned  decrease  in  state 
of  oxidation,  as  high  temperatures  convert  Mn02  into  Mn304  and 
Mn203,  each  of  which  is  partially  soluble  in  nitric  acid.  Therefore 
heat  would  tend  to  increase  the  solubility  in  nitric  acid  of  that  portion 
occurring  as  Mn02. 

In  addition,  it  is  known  that  the  action  of  heat  upon  organic  com- 
pounds of  manganese  and  also  certain  of  its  salts  converts  them  into 

i  MnjO<— 2  Mno+MnOj;  MnI08=MnO  +  MnOj.    Hence  it  may  be  observed  that  MnjO«  contains  the 
more  soluble  manganese. 

14000°— Bull.  30—13 3 


18 

oxids.     Then,  apparently  the  more  soluble  oxid,  Mn304,  is  formed  in 
greater  amounts  when  the  soil  is  heated  to  250°  C. 

LIME   AND   MAGNESIA. 

The  two  tables  below  show  the  effects  of  heat  upon  the  solubility 
of  lime  and  magnesia : 

Solubility  of  lime  in  water  and  fifth-normal  nitric  acid. 
[Calculated  on  basis  of  dry  soiL] 


Soil  No. 

Soluble  in  water  (parts  per  million). 

Soluble  in  fifth-normal  nitric  acid  (per 

cent). 

Air  dry. 

Dried  at 
100°  C. 

Dried  at 
250°  C. 

Ignited. 

Air  dry. 

Dried  at 
100°  C. 

Dried  at 
250°  C. 

Ignited. 

74 

176.8 

28.1 

224.  9 

112.6 

183.0 

296.9 

82.2 

26.5 

57.1 

184.4 

16.1 

59.2 

330.6 

44.2 

302.9 

86.9 

232.1 

133.3 

107.3 

98.5 

93.9 

1, 455. 6 

33.8 

67.1 

2,801.1 
64.3 
910.9 
242.3 
195.6 
363.0 
270.6 
330.5 
697.5 

1,509.3 
225.8 
763.6 

1,039.5 
38.1 
766.8 
207.1 
206.3 
261.9 
232.6 
332. 9 
547.7 
220.6 
106.1 
708.6 

2.312 
.026 
.448 
.147 
.378 
.344 
.159 
.174 
.388 
.466 
.056 
.248 

2.332 
.030 
.909 
.856 
.406 
.362 
.158 
.174 
.409 
.479 
.083 
.252 

2.131 

.024 
.511 
.986 
.318 
.330 
.124 
.167 
.329 
.395 
.056 
.226 

1.427 
.024 
.323 
.674 
.876 
.316 
.108 
.136 
.191 
.368 
.058 
.162 

L64 

9 

292 

290 

405 

416 

417 

406 

428 

426 

448 

Solubility  of  magnesia  in  water  and  fifth-normal  nitric  acid. 
[Calculated  on  basis  of  dry  soil.] 


Soil  No. 

Soluble  in  water  (parts  per 

million). 

Soluble  in  fifth-normal  nitric  acid  (per 
cent). 

Air  dry. 

Dried  at 
100°  C. 

Dried  at 
250°  C 

Ignited. 

Air  dry. 

Dried  at 
100°  C. 

Dried  at 
250°  C. 

Ignited. 

74 

75.1 

50.2 

96.4 

83.4 

285.2 

209.7 

105.1 

67.5 

82.2 

152.6 

34.6 

57.8 

73.9 

42.2 

99.5 

91.1 

385.2 

130.9 

127.5 

126.6 

87.2 

366.8 

47.4 

77.8 

182.7 
60.2 
167.3 
136.7 
230.3 
151.6 
140.9 
189.8 
234.7 
268.4 
158.1 
297.9 

63.1 

44.2 
150.4 
130.5 
192.6 
147.0 
127.5 
157.1 
245.9 
134.2 
108.4 
303.3 

0.121 
.019 
.071 
.150 
.500 
.206 
.073 
.071 
.204 
.114 
.047 
.074 

0.123 
.020 
.066 
.359 
.522 
.204 
.062 
.073 
.226 
.107 
.040 
.064 

0.138 
.021 
.081 
.344 
.301 
.140 
.042 
.049 
.115 
.082 
.041 
.048 

0.096 

164 

.019 

3 

.049 

292 

.197 

290 

.283 

405 

.060 

416 

.046 

417 

.062 

406 

.098 

428 

.079 

426 

.044 

448 

.048 

The  series  of  lime  determinations  shows  that  this  constituent  is 
most  soluble  in  water  in  the  soils  which  were  heated  to  250°  C. 
and  least  soluble  in  the  air-dried  soils.  This  is  true  of  every  sample 
except  one  (No.  290),  this  latter  being  a  peculiar  adobe  type  of 
soil  from  the  experiment  station  grounds.  In  dilute  nitric  acid  it 
will  be  observed  that  lime  is  most  soluble  in  those  soils  heated  to 
100°  C,  and,  unlike  the  water  extractions,  the  least  concentration 
is  obtained  from  the  ignited  soils.  Thus  it  is  shown  that  the  action 
of  nitric  acid  in  no  way  correlates  with  that  of  distilled  water.  How- 
ever, the  results  show  the  more  highly  organic  soil  to  contain  lime 


19 

in  such  form  as  to  be  more  soluble  in  weak  solvents,  No.  164,  a 
mineral  soil,  being  the  least  soluble.  Attention  is  also  called  to 
the  effect  of  cultivation  or  aeration  upon  the  solubility  of  lime  and 
magnesia,  namely,  that  the  cultivated  soils  contain  these  elements 
in  far  more  soluble  form. 

From  a  study  of  the  table  of  magnesia  determinations  it  is  evi- 
dent that  the  action  of  the  solvents  upon  this  element  is  quite  sim- 
ilar to  their  action  on  lime  as  regards  the  effects  of  heat,  but  that 
the  lime  is  very  much  the  more  soluble  both  in  water  and  in  dilute 
nitric  acid.  The  results  of  the  extractions  with  water  show  a  max- 
imum solubility  in  the  samples  heated  to  250°  C,  the  least  soluble 
magnesia  in  the  air-dry  samples.  This  exactly  correlates  with  the 
results  of  the  lime  determination.  The  solubility  in  dilute  nitric  acid 
does  not  correspond  so  closely,  but  the  general  tendency  is  similar 
in  that  the  air-dry  samples  and  those  dried  at  100°  C.  contain  this 
element  in  the  highest  state  of  solubility,  while  in  the  ignited  soils 
it  is  least  soluble.  An  important  fact  to  which  attention  is  called 
is  that,  although  most  of  the  soils  in  this  series  show  from  digestion 
with  hydrochloric  acid  (1.115  specific  gravity)  a  higher  magnesia  con- 
tent than  lime,  one  of  them  four  times  as  much,  yet  the  lime,  with 
very  few  exceptions,  is  considerably  more  soluble.  One  exception 
is  to  be  found  in  sample  No.  290,  which  represents  a  soil  having  a 
characteristic  soapy  property  indicating  the  presence  of  hydrous 
magnesium  silicate. 

The  effect  of  heat  on  the  solubility  of  lime  and  magnesia  is  more 
striking  than  in  case  of  the  other  elements.  It  is  highly  probable  that 
the  increased  concentration  of  the  water  extract  of  the  soil  heated  to 
100°  C.  over  the  air-dried  sample  is  produced  through  physical  causes, 
namely,  destruction  of  the  soil  film  and  delrydration  accompanied  by 
a  slight  decomposition  of  organic  matter.  On  the  other  hand,  the  soil 
when  heated  to  250°  C.  undergoes  more  completely  all  the  above  trans- 
formations as  well  as  decomposition  of  organic  matter.  Since  calcium 
and  magnesium  are  two  of  the  elements  universally  combined  with 
organic  matter,  there  necessarily  follows  an  increase  in  solubility  as 
a  result  of  the  more  complete  decomposition.  The  soils  showing  the 
greatest  solubility  of  these  elements  in  water  were  those  containing 
the  highest  organic  matter. 

The  decrease  in  solubility  of  lime  and  magnesia  in  water  and  in 
nitric  acid  at  250°  C.  and  ignition  is  hard  to  explain.  It  is  undoubt- 
edly partly  due  to  chemical  changes  in  the  soluble  forms  resulting 
from  the  decomposition  of  the  organic  matter  and  is  also  influenced 
by  the  decrease  in  exposed  surfaces  as  a  result  of  an  aggregation  of  the 
soil  particles  and  probably  other  physical  factors.  It  is  suggested 
that  one  of  the  chemical  changes  taking  place  as  a  result  of  heat  is 
that  of   a  replacement  of  the  potash  and  soda  in  the  silicates  by 


20 

magnesia  and  lime,  more  particularly  the  latter.  The  data  in  the 
tables  show  a  decrease  in  solubility  of  lime  and  an  increase  in  that  of 
potash  upon  ignition  in  a  majority  of  the  samples.  In  addition  to  the 
above-mentioned  factors  a  decrease  in  solubility  after  ignition  would 
be  produced  by  the  conversion  of  the  bicarbonates  into  normal  car- 
bonates, the  former  of  which  are  more  soluble  than  the  latter.  This 
would,  of  course,  be  most  striking  in  the  water  extracts. 

POTASH. 

'  The  following  table  shows  the  relative  effects  of  heat  upon  the  solu- 
bility of  potash: 

Solubifity  of  potash  in  water  and  fifth-normal  nitric  acid. 
Calculated  on  basis  of  dry  soil.] 


Soil  No. 

Soluble  in  water  (parts   per 

million). 

Soluble .  in  fifth-normal  nitric  acid  (per 
cent). 

Air  dry. 

Dried  at 
100°  c. 

Dried  at 
250°  C. 

Ignited. 

Air  dry. 

Dried  at 
100°  C. 

Dried  at 
250°  C 

Ignited. ; 

74     

128.2 
64.3 

117.8 
77.2 
87.1 
96.6 

"98.2 
60.3 
36.5 

£44.8 
43.8 

119.8 

117.4 

82.3 

192.7 
76.3 
92.4 
55.1 
96.2 

100.8 
49.2 

202.8 
58.7 

107.4 

339.3 
40.1 

301.9 

118.0 
90.6 
45.9 
78.3 
77.4 
19.4' 

353.5 
56.4 
64.4 

217.5 

132.5 

260.6 

•        83.8 

.77.4 

43.6 

147.6 

140,6 

.    78.2 

220.7 

182.9 

59.0 

0.053 
.027 
.073 
.061 
.177 
.  056 . 
.055 

•   .061 
.014 
.0:38 
.025 
.032 

0.066 
'.032 
.081 
.  155 
.142 
.084 
.056 
.0,54 
.013 
.051 
.024 
.032 

0.050 
.026 
.064 
.202 
.054 
.095 
.038 
.038 
.032 
.029 
.030 
.033 

0.068 

i  4           

.071 

.113 



|92          

.134 

290       . . .' 

.094 

405 

.090 

416       

.062 

417       ' 

.072 

406 

.022 

428       

.041 

426      

.070 

448 

.053 

.  The  figures  ■show  that  the  effect  of  heat  upon  potash  is  slightly 
different  from -the  effects  on  lime  and  magnesia.  The  ignited  soils 
appear  to  contain  this  element  in  the  most  soluble  form,  while  the 
samples  dried  in  air  and  at  100°  C.  contain  it  in  the  least  soluble 
form.  In  the  air-dried  samples  potash  is  also  more  soluble  in  the 
cultivated  than  in  the  uncultivated  soil,  and  the  greatest  solubility 
of  this  element  is  also  found  in  the  highly  organic  soils. 

Soils  in  general  possess  fixing  power  for  potash  and  for  phos- 
phoric acid  in  particular.  The  fixing  of  potash  is  generally  believed 
to  be  due  to  hydrated  silicates  and  organic  matter.  Cameron  and 
Bell 1  on  continuously  extracting  a  soil  with  water  until  no  more 
potash  dissolved,  then  grinding  the  sample  and  reextracting,  found 
an  additional  amount  of  potash  to  be  removed.  This  they  attributed 
to  a  colloidal  aluminum  silicate  upon  the  surface  of  the  particles, 
thus  protecting  them  from  the  action  of  the  water  as  well  as  absorb- 
ing the  potash.  Dehydration  and  decomposition  would  therefore 
materially  overcome  the  fixing  power,  and  the  potash  replaced  by 
lime  or  magnesia  would  not  be  refixed  during  a  short  period. 

'  U.  S.  Dept.  Agr.,  Bur.  Soils  Bui.  30,  p.  26. 


21 


•  PHOSPHORIC    ACID. 

i  In  the  next  table  are  shown  the  results  of  the  action  of  heat  on  the 
Solubility  of  phosphoric  acid.- 

Solubility  of  phosphoric  acid  in  water  and  fifth-normal  nitric  acid. 
iCalculated  on  basis  of  dry  soil.] 


Soil  No. 

Soluble  in  water  (parts  per 

million). 

Soluble  in  fifth-normal  nitric  acid  (per 
cent). 

Air  dry. 

Dried  at 
100°  C. 

Dried  at 
250°  C. 

Ignited. 

Air  dry. 

Dried  at 
100°  C. 

Dried  at 
250*  C 

Ignited. 

7-1 

264 

g 

39.8 

24.1 

17.1 

21.9 

22.9 

27.1 

36.5 

54.3' 

23.4 

2.5.6 

25.4 

29.6 

69.6 
36.1 
44.5 
26.9 
36.5 
31.0 
43.6 
52.7 
35.7 
38.7 
24.8 
36.2 

58.7 
16.1 
52.9 
23.8 
25.8 
33.0 
49.2 
46.8 
21.2 
26.8 
27.1 
37.6 

32.6 
15.1 
32.8 
22.8 
27.9 
25.3 
51.4 
39.8 
23.4 
23.8 
27.1 
28.1 

0.007 
.005 
.007 
.058 
.006 
.011 
.005 
.005 
.024 
.011 
.008 
.028 

0.008 
.006 
.007 
.018 
.016 
.014 
.007 
.008 
.030 
.013 
.012 

•   .028 

0.024 
.007 
.011 
.020 
.020 

-.027 
.007 
.009 
.064 
.012 
.011 
.036 

0.043 

.00'J 
.013 

2D2 

290 

40.5 

416 

417 

.053 
.031 
.021 
.006 
.005 

406 

.047 

428 

.014 

426 

.013 

44S 

.020 

It  may  be  seen  from  this  table  that  the  solubility  of  phosphoric 
acid  is  materially  affected  by  heat,  the  solubility  in  water  being 
greatest  in  the  soils  heated  to  100°  and  250°  C,  if  it  be  permissible 
to  draw  conclusions  from  the  general  averages,  while  it  is  least  soluble 
in  the  air-dried  soils.  It  is  also  worthy  of  note  that  this  element  is 
more  soluble  in  the  uncultivated  than  the  cultivated  soil,  the  former, 
however,  decreasing  with  increase  in  heat.  In  the  extractions  made 
with  dilute  nitric  acid  the  average  indicates  a  greater  solubility  in 
the  ignited  soils,  the  solubility  tending  to  increase  with  increase  in 
temperature. 

Phosphoric  acid  exists  in  soils  in  major  part  combined  with  iron, 
aluminum,  magnesium,  and  calcium,  and  is  also  found  combined  with 
organic  matter,  being  always  present  in  the  so-called  humus  of  soils. 
It  may  be  in  the  form  of  basic  phosphates,  hydrogen  phosphates,  or  as 
complex  phosphates  in  combination  with  more  than  one  element. 
It  is  probably  combined  mostly  with  iron  and  aluminum  and  titanium 
in  Hawaiian  soils.  Considerable  work  has  been  done  upon  the  effect 
of  heat  upon  the  solubility  of  this  constituent  and  several  attempts 
have  been  made  to  draw  conclusions  from  these  results  as  to  its  state 
of  combination;  that  is,  whether  organically  or  inorganically  com- 
bined. Peterson ■  using  fifth-normal  nitric  acid  found  that  after 
oxidizing  the  organic  matter  with  hydrogen  peroxid  there  was  no 
increase  in  the  solubility  of  phosphoric  acid  when  the  soil  was  heated 
to  240°  C.  He  concluded,  therefore,  that  the  solubility  of  mineral 
phosphates  in  soils  is  not  increased  up  to  240°  C.  The  author's  results 
tend  to  indicate  a  decrease  in  solubility  of  phosphoric  acid  at  high  tem- 

'  Wisconsin  Sta.  Research  Bui.  19 


22 


peratures,  due  either  to  a  chemical  change  in  its  combination  to  a  form 
less  soluble  in  water  or  an  increase  in  the  absorbing  power  of  the  soil. 
The  increase  effected  at  100°  and  250°  C.  is  undoubtedly  partly  due  to 
destruction  of  organic  matter  and  to  the  breaking  up  of  the  colloidal 
film.  The  action  of  dilute  nitric  acid  is  somewhat  different,  in  that 
an  increase  in  solubility  upon  ignition  accompanies  that  of  iron, 
alumina,  silica,  and  titanium.  Iron  and  aluminum  in  Hawaiian  soils 
occur  in  the  form  of  hydrates  to  a  certain  extent  and  are  more  or  less 
impregnated  with  the  phosphoric  acid  and  titanium  oxid,  not  only 
holding  them  in  chemical  combination,  but  also  mechanically.  The 
effect  of  heat  would  directly  increase  the  solubility  of  these  con- 
stituents in  dilute  nitric  acid  gradually  up  to  the  point  of  ignition, 
at  which  point  the  decomposition  of  the  hydrates  would  be  at  a 
maximum.  Changes  due  to  the  destruction  of  organic  matter  would 
cause  an  increase  in  the  solubility  of  this  element.  Another  factor 
of  some  importance  in  this  connection  is  that  of  precipitation  subse- 
quent to  solution.  The  increased  solubility  of  aluminum  and  man- 
ganese would  probably  produce  some  precipitation  of  phosphoric 
acid,  particularly  in  the  water  extract. 


SULPHATES. 


The  following  table  shows  the  solubility  of  sulphates   (S03)  as 
affected  by  heat: 


Solubility  of  sulphuric  acid  in  water  and  fifth-normal  nitric 
[Calculated  on  basis  of  dry  soil.| 

acid. 

Soil  No. 

Soluble 

n  water   (parts  per  million). 

Soluble  in  fifth-normal  nitric  acid  (per 
cent). 

Air  dry. 

Dried  at 
100°  C. 

Dried  at 
250°  C. 

Ignited. 

Aix  dry. 

Dried  at 
100°  C. 

Dried  at 
250°  C. 

Ignited. 

74 

172.4 
72.3 
111.4 

164.7 

100.  2 

129.  6 

59.4 

98.9 

2C.0. 3 

494.8 

46.2 

110.0 

130.5 

66.2 
146.2 
159.5 
176.2 
149.3 
100.6 
103.1 
326.4 
2, 123.  7 
54.2 
107.4 

1,961.6 
206.7 

1,339.7 
722.5 

1,128.3 
942.0 
702.3 
872.1 

1,555.9 

2, 598. 0 
119.7 

1,621.3 

1,309.2 
168.6 

1,294.4 
532.3 
799.5 
583.6 
664.3 
926.0 

1, 479. 9 
680.1 
241.6 

1,575.7 

0.027 
.037 
.017 
.067 
.022 
.018 
.028 
.032 
.061 
.089 
.018 
.028 

0.019 
.031 
.019 
.018 
.026 
.016 
.035 
.032 
.086 
.073 
.034 
.029 

0.106 
.027 
.053 
.019 
.062 
.067 
.038 
.037 
.163 
.101 
.019 
.044 

0.067 

164 

.025 

9 

.034 

292 

.055 

290 

.063 

405 

.048 

416 

.041 

417 

.052 

406 

.187 

428 

.177 

426 

.024 

448 

.122 

It  will  be  seen  from  this  table  that  the  effect  of  heat  upon  the  solu- 
bility of  the  sulphates  is  quite  marked,  more  so  in  the  water  extracts. 
In  this  series  the  air-dried  soil  is  the  least  soluble,  that  dried  at  100°  C* 
next,  while  the  maximum  solubility  is  reached  at  about  250°  C,  de- 
creasing upon  ignition.  On  the  other  hand,  the  solubility  in  dilute 
nitric  acid  is  slightly  different  in  that  the  average  shows  the  maximum 
solubility  to  be  obtained  from  the  ignited  samples,  the  least  soluble 
being  in  the  oven-dried  (100°  C.)  soil.  The  surprising  feature  of  these 
results  is  the  markedly  greater  solubility  of  sulphates  in  water  than  in 


23 

nitric  acid  as  shown  in  a  number  of  instances,  This  is  probably  due 
to  precipitation  subsequent  to  extraction  in  the  nitric  acid  extracts. 
Part  of  the  increase  in  the  solubility  of  sulphates  in  the  heated 
soils  of  this  series  was  probably  due  to  absorption  of  the  products  of 
combustion  of  the  gas  used  in  heating  the  oven.  It  was  found  that 
by  passing  the  products  of  combustion  through  water  a  precipitate 
of  barium  sulphate  was  obtainable  upon  the  addition  of  barium 
chlorid.  King1  found  an  enormous  increase  in  the  solubility  of 
sulphates  upon  heating  in  an  oven  at  110°  C.  using  both  gasoline  and 
kerosene  as  a  source  of  heat,  thus  largely  eliminating  this  factor. 
In  spite  of  the  possibility  of  an  introduction  of  error  due  to  this 
cause  it  is  probable  that  the  results  tabulated  here  disclose  correctly 
the  effect  of  heat  upon  the  sulphates.  In  addition  to  the  already- 
mentioned  reasons,  namely,  destruction  of  organic  matter,  soil  films, 
etc.,  it  is  necessary  to  take  into  consideration  the  chemical  effect  of 
heat  upon  the  various  mineral  sulphur  compounds.  Calcium  sulphate 
is  known  to  exist  in  four  forms,  two  being  anhydrous,  one  of  which  is 
more  soluble  than  the  other.  Sulphur  also  exists  in  soils  as  sulphids 
generally  combined  with  iron,  or  as  sulphates  in  combination  with  iron, 
lime,  or  magnesia,  also  combined  with  organic  matter  in  many  essential 
forms.  The  effect  of  heat  would  be  most  marked  upon  the  latter  in 
that  it  would  undergo  considerable  decomposition  at  250°,  the  sulphur 
being  oxidized  to  sulphur  dioxid  or  trioxid,  which  upon  treatment 
with  water  as  a  solvent  would  tend  to  form  sulphuric  acid  or  sulphates 
to  the  extent  of  the  bases  in  solution.  On  the  other  hand,  it  is  evident 
that  large  amounts  of  sulphur  will  be  lost  through  volatilization  upon 
ignition.  Soil  Xo.  428,  a  highly  organic  soil,  illustrates  this  effect 
best  in  that  the  increase  from  air  dried  to  oven  dried  (100°  C.)  is 
1,600  parts  per  million,  while  the  decrease  from  the  sample  heated 
from  250°  C.  to  ignition  is  1,900  parts  per  million.  It  is  evident 
from  these  data  that  upon  igniting  the  soils  the  sulphur  set  free  from 
the  destruction  of  the  organic  matter  is  oxidized  and  volatilized  so 
that  it  is  lost  before  combination  with  the  bases  takes  place. 


BICARBONATES. 

The  following  table  shows  the  bicarbonate  content  of  the  water 

extracts : 

Solubility  of  bicarbonates  in  water. 

(Parts  per  million  of  dry  soil.) 


Treatment  of  soil. 

Soil 
No. 
74. 

Soil 
No. 
164. 

Soil 
No. 
9. 

Soil 
No. 
292. 

Soil 
No. 
290. 

Soil 
No. 
405. 

Soil 
No. 
416. 

Soil 
No. 
417. 

Soil 
No. 

406. 

Soil 
No. 
428. 

SoU 
No. 
426. 

370.1 

44S.O 

1,309.2 

314.2 

106.4 
137.4 
91.3 
45.1 

113.5 
419.4 
338.9 
230.9 

158.5 
283.7 
363.5 
252.1 

132.9 

202.7 

327.7 

70.9 

161.4 
297.5 
157.3 
174.6 

35.4 
221.4 
1533 

73.8 

73.6 
2X6.0 
143.0 

53.9 

52.5 
136.4 

68.2 
118.5 

73.1 
204.3 
582.8 
133. 1 

70.5 

Dried  at  100°  C 

Dried  at  2.'*)°  C 

Ignited 

102.7 
SflS.  4 
MD.fi 

(7.  S.  Dopt.  Iff.,  Bur.  SoiLs  Bui.  26  p.  56 


24 


The  results  herewith  shown  are  not  very  consistent,  but  the  average 
ndicates  the  maximum  solubility  of  carbonic  acid  to  be  in  the  samples 
treated  to  100°  and  250°  C,  indicating  that  drying  has  the  effect  of 
increasing  the  amounts  of  bicarbonates  in  the  soil  and  thus  increasing 
the  solubility  of  the  bases  with  which  carbonic  acid  combines.  One' 
reason  suggested  in  the  above  table  for  a  decrease  in  water  soluble 
constituents  upon  ignition  is  that  ignition  would  cause  a  transforma- 
tion of  the  bicarbonates  into  normal  carbonates,  therefore  temporarily 
reducing  their  solubility  in  water. 

At  the  beginning  of  this  work .  some  determinations  of  titanium 
were  made,  but  these  were  not  carried  through  the  series.  This 
element  was  not  present  in  the  water  extract  in  large  enough  quantities 
to  be  determined.  In  the  dilute  nitric  acid  extracts  it  was  present  in 
very  small  amounts  in  the  samples  dried,  in  air  and  at  100°  C,  but  in 
much  larger  quantities  in  the  extracts  from  samples  heated  to  250°  C. 
and  ignition,  the  maximum  solubility  being  obtained  upon  the  ignited, 
samples. 

EFFECT   OF    HEAT   UPON   RICE   AND   TARO    SOILS. 

In  the  following  table  is  shown  the  effect  of  heat  upon  the  soils  used 
in  aquatic  agriculture,  comparing  this  with  the  solubility  of  the 
elements  in  the  wet  and  soggy  condition: 


Effect  of  heat  upon  soils  used  in  aquatic  agriculture. 
[Parts  per  million  of  dry  soil  water  extract.] 

Condition  of 
sample. 

Silica 
(Si02). 

Alu- 
mina 

(A1203). 

Iron 

oxid 

(Fe203). 

Manga- 
nese 
oxid 

(Mn30<). 

Lime 
(CaO). 

Mag- 
nesia 
(MgO). 

Potash 

(K20). 

Phos- 
phoric 
acid 
(P2O5). 

Sul- 
phuric 

acid 
(S03). 

Bicar- 
bonates 
(HCO3). 

Rice  soil,  No.  405: 
Wet 

6.9 
2.3 

.6.9 

5.7 
16.1 

36.6 
4.6 

4.5 

31.2 
33.5 

5.6 
7.6 

13.8 

17.6 
12.2 

62.4 
10.3 

19.6 

28.5 
38.0 

12.2 
6.4 

9.2 

■    5.4 
5.1 

86.1 
4.6 

2.7 

4.0 
2.1 

64.7 
5.9 

10.3 

14.9 
18.4 

34.4 
9.1 

4.4 

6.0 
9.6 

664.8 
296.9 

133.3 

363.0 
261.9 

318.6 
57.1 

93.9 

697.5 
547.7 

458.7 
209.7 

130.9 

151.6 
147.0 

310.0 
82.2 

87.2 

234.7 
245.9 

111.9 
96.6 

55.1 

45.9 
43.6 

31.8 
36.5 

49.2 

19.4 

78.2 

43.7 
27.1 

31.0 

33.0 
25.3 

38.7 
23.4 

35.7 

21.2 
23.4 

153.9 
129.6 

149.3 

942.0 
583.6 

137.8 
260.3 

326.4 

1,555.9 
1,479.9 

328  9 

Air  dry 

Dried  at  100° 
c 

161.4 
297.5 

Dried  at  250° 
c 

157.3 

Ignited 

Tarosoil,No.  406: 
Wet 

174.6 
294.9 

Air  dry 

Dried  at  100° 
c 

52.5 
136.4 

Dried  at  250° 
c 

68.2 

Ignited 

118.5 

When  the  types  of  soil  were  chosen  for  use  in  this  series,  two  were 
selected  with  a  view  to  obtaining  some  information  upon  the  soils 
in  use  for  rice  and  taro  culture.  It  would  be  expected  that  heat  and 
its  accompanying  oxidation  would  have  a  marked  effect  upon  this 
type  of  soil  for  the  reason  that  for  the  most  part  it  exists  in  a  reduc- 
ing environment.  The  above  table  shows  solubility  in  water  only. 
The  samples  were  taken  from  the  field  in  wet  condition  and  extrac- 
tions were  made  upon  weighed  samples  immediately  upon  receipt 
in  the  laboratory,  the  moisture  content  in  this  state  being  about 


25 

50  per  cent.  This  table  discloses  the  high  concentration  of  soluble 
plant  food  in  these  soils  under  the  reducing  conditions.  While  the 
mineral  constituents  tend  to  increase  in  solubility  with  increase  in 
heat  with  relation  to  the  air-dry  samples,  a  maximum  solubility  is 
obtained  from  the  wet  samples  in  the  case  of  the  iron,  manganese, 
lime,  magnesia,  phosphoric  acid,  and  bicarbonates,  and  in  one  of 
the  samples  a  maximum  solubility  is  obtained  for  the  remaining 
constituents,  silica,  alumina,  and  potash.  Therefore,  these  results 
indicate  that  the  effect  of  drying  and  heating  the  soils  used  in  aquatic 
agriculture  does  not  increase  the  solubility  of  the  mineral  constitu- 
ents over  and  above  the  solubility  in  the  wet  state  but  rather  brings 
about  a  decrease  in  all  constituents  except  sulphates. 

The  concentration  of  the  extracts  from  these  soils  in  the  wet  state 
does  not  necessarily  indicate  that  the  mineral  constituents,  with  the 
exception  of  iron,  are  actually  more  soluble  than  those  of  dry-land 
soils.  Neither  should  we  conclude  that  the  abnormal  concentra- 
tion is  wholly  due  to  more  complete  diffusion  coupled  with  greater 
solubility  induced  by  the  environment  to  which  these  soils  are  sub- 
jected. The  amount  of  water  always  present  in  these  soils  is  far  in 
excess  of  that  occurring  in  dry-land  soils,  and  since  there  necessarily 
must  be  a  tendency  toward  constancy  in  concentration  regardless 
of  the  amount  of  solvent  present,  in  time  the  absolute  amounts  of 
solids  going  into  solution  would  be  considerably  greater  in  submerged 
•soils.  The  moisture  content  of  these  two  soils  when  received  at  the 
laboratory  was  about  50  per  cent,  whereas  the  dry-land  soils  contain 
very  much  less  moisture.  The  water  extracts  obtained  by  the 
methods  employed,  therefore,  would  necessarily  contain  greater 
absolute  amounts  of  substances  already  in  solution  in  the  soil  water. 
Hence  the  concentration  of  the  nutrient  solution  occurring  in  sub- 
merged soils  need  not  necessarily  be  greater  than  that  of  dry-land 
soils. 

DISCUSSION. 

The  foregoing  results  show  that  an  increase  in  solubility  of  the 
mineral  constituents  of  various  types  of  Hawaiian  soils  is  effected 
by  heating.  The  samples  represent  most  of  the  normal  and  abnormal 
types  of  the  islands.  That  there  are  both  chemical  and  physical 
factors  concerned  in  the  phenomena  at  hand  must  be  admitted  at 
the  outset.  It  is  believed,  however,  that  the  most  important  set 
of  factors  affecting  the  solubility  of  inorganic  soil  constituents  are 
of  a  physical  nature. 

Undoubtedly  the  means  by  which  the  physical  factors  act  is  through 
the  soil  moisture  in  its  relation  to  the  physical  properties  of  the  soil. 
The  conditions  conducive  to  the  formation  of  a  colloidal  state  and  the 
subsequent  relation  of  heat  to  the  destruction  of  this  colloid  are  two 
of  the  most  important  of  these  factors. 


26 

It  is  certain  that  soil  moisture  distributes  itself  around  the  soil 
particles  and  in  some  instances  as  an  impregnation  within  the  par- 
ticles. The  moisture  therefore  occurs  as  thin  films  which,  according 
to  certain  physical  conceptions,  must  be  held  around  the  particle  by 
an  enormous  pressure.  From  purely  physical  considerations  this 
pressure  has  been  estimated  at  several  thousand  atmospheres.  Under 
such  pressure  the  concentration  of  film  water  with  reference  to  the 
mineral  matter  should  be  much  greater  than  that  of  the  free  or 
capillary  water  in  the  soil. 

Then  the  air-dried  soil,  the  particles  of  which  are  still  surrounded 
by  a  film  of  moisture,  when  shaken  with  water,  should  theoretically 
show  the  least  solubility.  The  results  reported  in  this  bulletin  in 
most  instances  are  in  harmony  with  this  assumption.  But  if  the  soil 
be  allowed  to  remain  in  the  condition  and  environment  prevailing  in 
submerged  cultures,  that  is,  in  the  presence  of  a  large  excess  of  water, 
then  in  time  diffusion  would  bring  about  a  more  or  less  equal  distribu- 
tion of  dissolved  materials  throughout  the  entire  water  present  and 
the  pressure  of  soil  films  would  be  decreased  to  a  minimum  or  entirely 
eliminated.  Hence  the  amount  of  materials  going  into  solution  in 
the  free  water  in  such  soils  would  be  expected  to  be  abnormally  high. 
Upon  air  drying  such  soils  the  normal  films  would  again  appear  with 
a  resulting  decrease  in  solubility.  Subsequent  heating  ought  then 
to  affect  these  soils  in  a  way  similar  to  that  produced  on  dry-land 
soils.  The  data  presented  in  the  previous  tables  are  again  in  harmony 
with  this  view. 

Water,  however,  not  only  exercises  a  solvent  action  on  minerals 
but  forms  various  hydrates,  the  solubility  and  physical  character  of 
which  in  some  instances  are  greatly  altered ;  organic  as  well  as  inor- 
ganic matter  goes  into  solution  with  the  result  that  the  moisture  films 
around  the  particles  became  solution  films,  holding  in  suspension  and 
more  or  less  intermingled  with  colloids,  both  organic  and  inorganic. 
The  films  then  may  be  looked  upon  as  being  of  a  colloidal  nature.1 

Upon  heating  to  100°  C.  alterations  in  the  films  would  take  place 
through  evaporation  and  by  partial  dehydration  of  colloids,  thus  de- 
stroying the  pressure  by  which  the  film  was  previously  held  around 
the  particles.  At  the  temperature  of  100°  C.  the  concentration  of  the 
soil  moisture  would  also  be  temporarily  increased,  due  to  increase  in 
solubility  with  heat.  During  the  course  of  the  evaporation  the  con- 
centration of  the  soil  moisture  would  increase  to  the  saturation  point, 
after  which  the  mineral  matter  would  be  deposited  on  the  surface  of 
the  film  as  evaporation  went  on.2  Also  the  materials  held  in  solution 
in  the  interior  of  the  permeable  particles  would  be  partially  deposited 

i  No  claim  is  made  for  originality  in  this  view.    The  idea  of  soil  films,  colloidal  films,  etc.,  has  been  made 
use  of  by  various  writers  on  soils. 
*  King  (loc.  cit.)  in  discussing  the  relative  solubilities  of  fresh  and  dried  soils  advanced  this  idea. 


27 

on  the  surface  of  the  water  evaporated.  Upon  adding  water  to  the 
soil  after  having  been  dried,  it  is  probable  the  materials  deposited 
from  previous  evaporation  would  be  more  soluble  than  the  other 
mineral  constituents.  In  addition  a  certain  amount  of  oxidation 
and  other  chemical  changes  in  the  organic  matter  might  reasonably 
be  expected  to  take  place,  which  would  have  some  effect  on  the 
solubility  oi  the  mineral  bases  that  tend  to  combine  with  the  organic 
matter. 

The  solution  obtained  upon  shaking  with  water  a  soil  previously 
dried  should,  in  the  light  of  these  views,  be  of  a  greater  concentration 
than  that  prepared  from  the  air-dried  soil.  With  the  absence  of  soil 
films  and  a  more  or  less  altered  condition  of  the  colloids  present  the 
solvent  would  have  more  ready  access  to  the  soil  particles  during  a 
short  period  in  addition  to  coming  into  immediate  contact  with 
solids  deposited  on  the  surface  of  the  particles. 

Why  several  of  the  mineral  constituents  of  the  soil  should  be  so 
markedly  more  soluble  when  heated  to  250°  C.  than  at  the  other 
temperatures  is  a  question  not  easily  answered.  The  difference  in 
physical  effects  were  quite  noticeable  in  that  there  was  a  greater 
aggregation  of  particles.  Again,  there  was  a  more  complete  destruc- 
tion of  organic  matter  effected  at  this  temperature,  and  also  it  is  not 
entirely  impossible  that  drying  at  100°  C.  for  eight  hours  does  not 
effect  a  complete  elimination  of  the  soil  moisture  and  especially  the 
water  of  chemical  combination.  It  seems  reasonable,  then,  that  the 
effects  of  heating  to  100°  C.  are  simply  magnified  when  heated  to 
250°  C.  Added  to  this  there  is  a  more  complete  destruction  of  organic 
matter,  the  effect,  both  physical  and  chemical,  being  of  the  same 
general  nature  but  more  complete  at  the  higher  temperature.  The 
destruction  of  organic  constituents  being  more  complete  would  neces- 
sarily increase  the  solubility  of  the  mineral  matter  held  in  combination, 
as  it  is  generally  conceded  that  the  organic  constituents  of  the  soil 
in  its  natural  state  are  quite  insoluble  in  water  and  acids,  more 
especially  in  the  former.  There  is  also  evidence  of  the  existence  of 
fatty  or  resinous  organic  matter  which  would  materially  affect  the 
properties  of  the  soil  film.  For  the  decomposition  of  such  bodies  it 
would  be  necessary  to  heat  the  soils  considerably  above   100°  C. 

In  addition  to  the  above-mentioned  effects  of  heat  the  relation 
between  solid  and  solvent  would  naturally  be  affected  by  other  factors. 
Among  these  is  the  absorption  or  "fixing  power"  of  the  soil.1  It  is 
reasonable  to  expect  soils  with  widely  varying  physical  and  chemical 
properties,  such  as  those  used  in  this  series,  to  differ  greatly  in 
absorptive  power.  Hence  it  is  not  at  all  unlikely  that  the  lack  of 
consistency  in  some  of  the  results  in  the  foregoing  tables  is  due 
primarily  to  this  factor.     Not  only  is  there  lack  of  uniformity  in 

i  Richter  (Landw.  Vers.  Stat.,  47  (1896),  p.  269)  found  that  heating  increased  the  absorptive  power  oi 
the  soil  for  water. 


28 

the  absorptive  power  of  soils,  but  they  also  show  considerable  selective 
power  in  the  absorption  of  mineral  constituents.  Soils  high  in 
humus  have  a  high  fixing  power,  due  to  the  ability  of  humus  to 
combine  chemically  with  minerals,  as  well  as  its  power  of  absorption, 
and  therefore  the  effect  of  heat  upon  highly  organic  soils  should  tend 
to  increase  the  solubility  of  the  minerals.  An  example  of  this  is  given 
in  the  cases  of  soils  Nos.  74  and  428.  Another  factor  is  that  of 
precipitation  following  extraction,  being  the  more  marked  in  the 
acid  extract  due  to  a  more  complete  extraction. 

In  passing  from  250°  C.  to  ignition  the  effects  are  apparently  of  a 
specific  rather  than  general  nature,  as  has  been  already  indicated. 
Among  these  effects  are  the  volatilization  of  certain  sulphur  com- 
pounds, conversion  of  bicarbonates  into  normal  carbonates,  de- 
hydration of  silicates,  etc.,  replacing  of  potash  by  lime,  and  other 
chemical  transformations.  In  addition  there  is  produced  a  greater 
aggregation  of  the  soil  particles,  resulting  in  a  decrease  in  surface 
area  exposed  to  the  solvent  and  an  accompanying  change  in  the 
fixing  and  absorbing  powers  of  the  soil.  It  is  possible,  by  application 
of  these  conceptions,  to  explain  the  majority  of  changes,  both  increase 
and  decrease  in  solubility,  resulting  from  ignition. 

THE  EFFECTS  OF  HEAT  ON  SOIL  NITROGEN. 
INTRODUCTION. 

The  data  presented  in  the  preceding  pages  indicate  the  existence 
of  colloidal  films  surrounding  the  soil  particles.  These  films  are 
probably  both  organic  and  inorganic  in  nature  and  undergo  altera- 
tion under  the  influence  of  heat.  By  such  alteration  new  surfaces 
become  exposed  to  the  action  of  solvents,  thereby  making  possible 
the  solution  of  materials  otherwise  effectively  protected  from  the 
solvents  used.  There  is  considerable  evidence  in  the  data,  however, 
that  other  changes  were  also  produced  by  the  heating.  Some  oxida- 
tions must  have  taken  place,  and  probably  decompositions  of  other 
types.  Changes  in  the  organic  matter  were  produced  at  the  higher 
temperatures,  as  shown  by  the  color  of  the  water  extracts. 

Theeffectof  heat  on  soil  organic  matter  has  been  the  subjectof  some 
previous  investigation.  It  has  been  observed,  for  example,  that 
water  extracts  from  heated  soils  are  usually  darker  in  color  and  con- 
tain greater  amounts  of  organic  matter  than  similar  extracts  from 
unheated  soUs. 

Darbishire  and  Russell l  found  that  plants  absorb  more  nitrogen 
from  soils  that  have  been  previously  heated  to  95°  and  120°  C.  than 
from  unheated  soils.  They  concluded  that  the  heating  brought  about 
some  decompositions  in  the  organic  matter  and  also  caused  a  modi- 
fication in  the  bacterial  flora. 

i  Jour.  Agr.  Sci.,  2  (1907),  p.  305. 


29 

Pickering  !  found  that  partial  sterilization  brought  about  an  in- 
crease in  the  solubility  of  the  organic  matter.  An  increase  in  the 
total  nitrogen  soluble  in  water  and  greater  absorption  of  nitrogen 
by  plants  were  also  produced  by  heating. 

Lyon  and  Bizzell 2  observed  that  the  action  of  steam  heat  at  2 
atmospheres  pressure  greatly  increased  the  ammonia,  in  addition  to 
increasing  the  water  soluble  inorganic  matter.  The  nitrates  were 
largely  decomposed  at  this  temperature  and  pressure. 

Russell  and  Hutchinson3  have  shown  that  by  heating  some 
Rothamsted  soils  at  98°  C.  for  three  hours  a  small  increase  in  the 
ammonia  content  took  place.  The  most  remarkable  effect  of  the 
partial  sterilization,  however,  was  in  connection  with  subsequent 
ammonification.  Ammonia  began  to  be  formed  in  the  course  of  a 
few  days,  followed  by  a  remarkable  production  of  ammonia  later  on. 
Corresponding  to  the  increase  in  ammonia  subsequent  to  heating, 
an  enormous  increase  in  the  numbers  of  microorganisms  (bacteria 
and  fungi)  took  place.  Heating  to  125°  also  caused  an  initial  pro- 
duction of  small  amounts  of  ammonia,  but  no  subsequent  ammonifi- 
cation set  in.  The  nitrates  were  little  affected  although  nitrification 
was  entirely  inhibited  by  the  treatment.  From  the  fact  that  volatile 
antiseptics  bring  about  similar  effects,  these  authors  believe  that 
partial  sterilization  kills  certain  biological  agents  which,  in  the 
untreated  soil,  effectively  hold  in  check  the  multiplication  and  activ- 
ity of  the  ammonifying  organisms.  After  these  inhibiting  agents 
are  destroyed  the  ammonifying  efficiency  of  the  soil  rises  rapidly, 
thus  making  available  greatly  increased  amounts  of  nitrogen. 

Lodge  and  Smith 4  found  that  decoctions  from  soils  show  an 
increase  in  ammonia  after  steam  sterilization  at  15  pounds  pressure, 
but  a  decrease  in  ammonia  took  place  from  the  sterilization  of  the 
subsoil. 

Lathrop  and  Brown 5  found  that  the  amounts  of  ammonia  and 
total  nitrogen  soluble  in  water  increased  with  an  increase  in  the 
pressure  under  which  the  soil  was  heated.  At  10  atmospheres 
approximately  40  per  cent  of  the  total  nitrogen  was  rendered  soluble, 
while  the  ammonia  thus  split  off  was  found  to  vary  from  7.83  per 
cent  to  15.64  per  cent. 

Recently  Schreiner  and  Lathrop 8  published  a  comprehensive 
investigation  of  the  effects  of  steam  heat  on  soil  organic  matter.  In 
this  work  they  isolated  from  heated  soils  a  number  of  compounds 
not  found  in  the  unheated  soil.     Among  the  compounds  isolated  a 

i  Jour.  Agr.  Sci.,  2  (1908),  p.  411. 

*  New  York  Cornell  Sta  Bui.  275  (1910). 
•Jour.  Agr.  Sci.,  3  (1909),  pp.  111-144. 

*  Massachusetts  Sta.  Rpt.  1911,  pt.  1,  pp.  126-134. 
•Jour.  Indus,  and  Engin.  Chem.,  3  (1911),  p.  657. 

6U.  S.  Dept.  Agv.,  Bur.  Soils  Bui.  89;  Jour.  Amer.  Chem.  Soc,  34  (1912),  pp.  1242-1259. 


30 

number  are  nitrogenous  and  it  is  of  special  interest  in  this  connection 
that-  practically  all  of  these  have  been  found  to  be  beneficial  to  plant 
growth.  Certain  nonnitrogenous  bodies,  however,  were  also  isolated, 
one  of  which,  dihydroxystearic  acid,  seems  to  have  been  formed 
under  the  action  of  heat  and  which  has  been  found  to  be  distinctly 
toxic  to  plants.1  It  has  been  known  for  some  time  that  steam  heat 
may  bring  about  toxic  conditions  in  soils,  apparently  of  an  organic 
nature,  but  it  remained  for  Schreiner  and  Lathrop  to  determine 
definitely  what  is  at  least  one  of  the  toxic  bodies  thus  produced. 
On  the  one  hand,  these  authors  have  shown  that  definite  nitrogen 
compounds  of  a  character  beneficial  to  plant  growth  are  formed  by 
the  action  of  heat,  while  on  the  other,  a  toxic  compound,  also  organic 
and  definite  in  character,  may  be  generated  at  the  same  time.  The 
significance  of  these  discoveries  is  at  once  apparent;  the  value  of 
such  definite  and  fundamental  data  can  not  fail  to  be  important. 

A  knowledge  of  the  effects  of  steam  heat  on  soil  organic  matter  has 
special  bearing  on  greenhouse  practices,  but  may  it  not  well  be  asked, 
what  are  the  effects  of  dry  heat  without  pressure  ?  This  phase  of  the 
question  has  not  been  exhaustively  studied.  It  is  unsafe  to  conclude 
a  priori  that  the  same  types  of  cleavage  and  hydrolysis  take  place  in 
the  absence  as  under  the  influence  of  pressure.  There  is  evidence  in 
the  growth  and  appearance  of  crops  on  burned  soil  that  nitrogen  is 
made  available  by  the  heat.  The  deep  green  color  of  the  crop  is 
sometimes  very  striking.  It  is  important,  therefore,  that  this  phase 
of  the  question  be  investigated  in  a  general  study  of  soil  heating  on 
account  of  the  importance  of  nitrogen  in  the  nutrition  of  plants. 

In  an  altogether  different  connection  our  attention  was  drawn  to 
the  very  large  increase  in  the  ammonia  of  some  Hawaiian  soils  brought 
about  by  the  action  of  heat.  It  was  observed  that  the  ammonia  con- 
tent of  certain  soils  increased  from  a  few  parts  to  over  400  parts  per 
million.  At  the  same  time  the  nitrates  were  decomposed.  From 
these  observations  and  its  general  bearing  on  soil  heating,  an  investi- 
gation of  the  nitrogen  transformations  seemed  of  interest  and  impor- 
tance. Whence  the  ammonia  thus  set  free  and  from  what  class  of 
compound  does  it  arise  ? 

The  nitrogen  of  soils  having  been  at  one  time  bound  up  in  organized 
tissue,  plant  and  animal,  and,  therefore,  largely  of  proteid  nature, 
undergoes  hydrolysis  under  the  action  of  enzyms,  bacteria,  etc.,  with 
the  resulting  formation  or  splitting  off  of  simpler  compounds.  In 
soils  there  must  occur  every  stage  of  these  changes  from  the  proteid 
complex,  on  the  one  hand,  to  inorganic  compounds,  on  the  other.  The 
larger  part  of  soil  nitrogen  exists,  however,  in  complex  organic  com- 
binations.    Nevertheless,  the  simple  inorganic  nitrogen  compounds, 

» U.  S.  Dept.  Agr.,  Bur.  Soils  Bui.  80  (1911). 


31 


especially  nitrates,  while  occurring  in  relatively  small  amounts,  have 
long  been  considered  to  be  of  great  importance  to  plant  growth. 

For  the  purposes  of  this  investigation  two  courses  of  procedure 
were  open.  First,  a  study  of  the  changes  that  take  place  in  the  indi- 
vidual nitrogen  compounds  occurring  in  soils;  second,  a  study  of  the 
group  changes — that  is,  the  effects  of  the  treatment  on  the  relative 
amounts  and  proportions  of  the  large  groups  included  under  the 
amids,  monamino  acids,  and'  diamino  acids.  The  latter  of  these  was 
chosen. 

EFFECTS  OF  HEAT  ON  NITRATES. 

The  soils  used  in  this  investigation  were  taken  from  various  locali- 
ties in  the  islands  and  represent  a  wide  range  of  types  and  conditions 
of  formation.  Some  of  the  samples  were  taken  from  arid  sections, 
some  from  intermediate,  and  still  others  from  extremely  humid  sec- 
tions. The  method  of  heating  differed  somewhat  from  that  employed 
in  the  work  already  reported.  The  time  of  heating  was  2  hours, 
and  the  temperatures  used  were  100,  150,  200,  250°  C.  and  steam  heat 
in  an  autoclave  at  2  atmospheres  pressure.  One  hundred  gram  por- 
tions of  air-dried  soil  placed  in  porcelain  dishes  were  heated  to  the 
desired  temperatures  in  an  air  bath,  or  autoclave.  Nitrates  were 
determined  colorimetrically  by  use  of  the  phenol  disulphonic  acid 
method,  and  ammonia,  from  separate  portions,  by  distillation  with 
magnesium  oxid  in  the  usual  way.  It  should  be  remembered  that 
the  ammonia  thus  obtained  probably  occurred  in  part  as  amids. 
Distillation  with  magnesium  oxid  is  known  to  liberate  ammonia 
from  amids.  In  a  lew  instances  the  modified  method  of  Schloesing,1 
which  consists  in  leaching  the  soil  with  dilute  hydrochloric  acid  and 
then  distilling  the  ammonia  from  the  filtrate  with  the  use  of  mag- 
nesium oxid,  was  employed.  The  results  were  very  similar  to  those 
obtained  by  direct  distillation.  The  following  table  shows  the  effects 
of  heat  on  the  nitrate  content : 

The  effects  of  heat  on  soil  nitrates. 
[Nitrate  nitrogen  expressed  in  parts  per  million  of  air-dried  soil.] 


Temperature. 

Soil 
No.  9. 

Soil 
No.  290. 

Soil 
No.  292. 

Soil 
No.  329. 

Soil 
No.  335. 

Soil 
No.  407. 

Soil 
No.  411. 

Soil 
No.  428. 

108.0 
95.0 

57.0 
5.0 
5.4 

94.0 

18.0 
18.6 
12.5 
6.5 
.5 

10.5 

17.6 
13.0 
23.5 
3.5 
1.4 

12.5 

197.0 

1.58.0 

61.5 

1.3 

3.5 

148.0 

3.3 
2.0 
3.0 
.6 
1.0 

L8 

0.7 
.7 
.6 
.5 
.4 

.6 

56.0 

60.0 

1.7 

1.5 

.5 

48.0 

70.0 

100°  c 

70.0 

150°C 

49.5 

200°C 

.8 

250°C 

.5 

Steam  pressure  2  at- 

46.0 

These  data  i 
on  soil  nitrates 

ire  of  interest 
.     In  most  in 

as  showing  the  destructive  effect  of  heat 
stances  the  nitrates  underwent  considera- 

i  Referred  to  by  Todidi,  Michigan  Sta.  Tech.  Bui.  4,  p.  1L 


32 

ble  decomposition  at  150°  C,  while  at  200  and  250°  C.  practically 
total  decomposition  took  place.  Heating  to  100°  C.  had  but  little 
effect.  Steam  heat  at  2  atmospheres  pressure  brought  about  some- 
what less  decomposition  than  dry  heat  at  150°  C. 


EFFECTS   OF   HEAT   ON   THE   AMMONIA    CONTENT. 

In  the  next  table  will  be  found  the  data  showing  the  effects  of  heat 
on  the  ammonia  content. 

Effects  of  heat  on  the  ammonia  content  of  soils. 
[Ammonia  nitrogen  expressed  in  parts  per  million  of  air-dried  soil.] 


Temperature. 

Soil 
No.  9. 

Soil 

No.  290. 

Soil 
No.  292. 

Soil 
No.  329. 

Soil 
No.  335. 

Soil 
No.  407. 

Soil 
No.  411. 

Soil 

No.  428. 

28.0 
23.8 
67.2 
187.6 
40.6 

83.3 

18.1 

19.6 

45.2 

464.8 

206.5 

51.1 

11.2 

10.5 

32.2 

174.3 

336.0 

16.8 

56.0 
64.4 
81.6 
218.4 
28.0 

77.7 

12.6 

18.2 
17.5 
32.2 
19.6 

16.1 

9.1 
13.5 

28.7 
368.2 
114.8 

46.2 

19.6 
28.0 
77.7 
170.8 
98.0 

69.2 

63  7 

oo°c 

72  8 

150°C 

127  2 

200°C 

274  4 

250VC 

238  0 

Steam  pressure,  2  at- 

112  7 

The  ammonia  content  of  soils  Nos.  329  and  428  before  heating  is 
here  shown  to  be  abnormally  high.  Generally  soils  contain  ammonia 
to  the  extent  of  a  few  parts  per  million  only,  whereas  the  nitrate  con- 
tent may  rise  to  considerable  concentration.1 

Under  the  influence  of  heat  the  ammonia  content  of  all  the  soils 
studied  was  greatly  increased,  practically  reaching  a  maximum  at 
about  200°  C.  Above  this  temperature  a  falling  off  took  place  which 
was  probably  due  to  a  loss  of  ammonia  through  volatilization.  We 
here  have,  therefore,  some  interesting  and,  as  seems  probable,  very 
important  facts.  As  pointed  out  above,  heat  considerably  increases 
the  solubility  of  the  inorganic  matter.  Here  it  is  shown  that  the 
ammonia  content  is  enormously  increased  also. 

Formerly  little  attention  was  given  to  the  ammonia  content  of  soils 
except  in  its  relation  to  nitrification.  During  the  past  few  years, 
however,  the  idea  that  ammonia  may  serve  as  a  direct  source  of  nitro- 
gen to  higher  plants  has  steadily  gained  ground.  It  is  now  known 
that  certain  aquatic  plants,  rice  in  particular,  not  only  can  utilize 
ammonium  nitrogen  but  that  this  form  of  nitrogen  is  better  adapted 
to  assimilation  by  rice  2  than  is  nitrate.  Other  crops  3  have  also 
been  found  to  be  able  to  transform   ammonia  into   proteids  with 

i  Ammonia  in  soils,  produced  by  biological  agents,  has  for  some  time  been  looked  upon  as  being  merely 
a  transitional  state,  its  formation  being  essential  to  nitrification.  The  nitrifying  organisms  seize  on  the 
ammonia  and  convert  it  into  nitrites  and  then  into  nitrates,  thus  effectively  preventing  an  accumulation 
of  ammonia  in  the  soil  at  any  one  time.  One  of  the  essentials  of  vigorous  nitrification,  however,  is  free 
oxygen,  while  ammonirication  may  take  the  place  under  anaerobic  conditions.  In  many  Hawaiian  soils 
aeration  is  very  low,  and  for  this  reason  (perhaps  others),  nitrification  frequently  does  not  keep  pace  with 
ammonification. 

2  See  Hawaiian  Sta.  Bui.  24. 

s  Kriiger,  Landw.  Jahrb.,  34  (1905),  No.  5,  p.  761. 


33 


equal  facility.  From  the  large  number  of  cultures  that  have  been 
reported  and  the  many  observations  made  it  is  safe  to  assume  that  the 
ammonia  of  natural  soils  is  absorbed  and  assimilated  to  a  greater  or 
less  extent  by  nearly  all  plants.  We  may  conclude,  therefore,  that 
an  important  part  of  the  action  of  heat  on  soils  has  to  do  with  the  pro- 
duction of  ammonia. 

As  previously  stated,  Schreiner  and  Lathrop  (page  29)  have  shown 
that  the  major  portion  of  the  organic  nitrogen  compounds,  split  off 
from  more  complex  bodies  in  soils  under  the  action  of  heat,  is  also 
beneficial  to  plant  growth.  With  the  additional  production  of  rela- 
tively large  amounts  of  ammonia  it  is  probable  that  marked  stimu- 
lation would  result. 

The  effect  of  heat  viewed  from  this  standpoint  is  also  of  interest  in 
its  relation  to  the  effects  of  partial  sterilization.  As  already  stated, 
one  of  the  pronounced  effects  of  partial  sterilization,  either  with  heat 
or  volatile  antiseptics,  is  the  abnormal  ammonification  thus  induced 
and  which  seems  to  be  correlated  with  marked  plant  stimulation. 
In  some  Hawaiian  soils  the  effect  of  partial  sterilization  on  subse- 
quent ammonification  has  recently  been  found  to  be  exceptionally 
great.  If  the  accumulation  of  ammonia  as  a  result  of  partial  sterili- 
zation reacts  beneficially  on  plants,  we  certainly  have  a  right  to  con- 
clude that  its  direct  production  by  means  of  heat  would  also  prove 
stimulative  to  crops. 

EFFECTS    OF   BRUSH    BURNING    IN    THE    FIELD. 

With  the  view  to  determining  the  effects  produced  by  burning 
refuse,  brush,  etc.,  in  the  field,  a  few  samples  of  soil  from  spots  where 
brush  had  been  burned  were  examined  at  two  different  times.  The 
brush  was  burned  about  September  1  and  the  samples  were  taken 
September  10  and  November  7,  respectively.  Care  was  taken  to 
remove  the  ashes  so  as  to  secure  portions  of  the  uncontaminated 
soil.  Samples  of  unburned  soil  near  by  were  taken  at  the  same 
time.     Ammonia  and  nitrates  were  determined  in  the  samples  as 

follows : 

Effects  of  burning  brush  on  soil  nitrogen. 
[Parts  per  million  of  nitrogen  in  air-dried  soil.] 


As  nitratos. 

As  ammonia. 

Laboratory  No. 

After  10 
days. 

Two 
months 
later. 

After  10 
days. 

Two 

months 

later. 

402  (burned ) 

6.5 

20.0 

•    6.0 

6.0 

16.0 

£2.0 

5.5 
18.0 
8.0 
8.0 
22.0 
52.0 

50.4 
39.2 
161.0 
21.0 
77.0 
8.4 

100.8 

402a  (not  burned; 

70.0 

403  (burned) 

10H.  4 

403a  (not  burned) 

32. 2 

404  (burned ) 

114  S 

30.8 

34 

Here  again  it  is  shown  that  an  increase  in  the  ammonia  and  a  de- 
crease in  nitrates  takes  place  in  soil  heating.  The  content  of  ammo- 
nia and  nitrates  at  the  end  of  two  months  is  of  special  interest.  The 
above  data  show  that  not  only  is  ammonia  formed  by  the  action  of 
heat  but  that  subsequently  ammonification  took  place  at  a  greater 
rate  in  two  cases  out  of  three  than  in  the  unburned  soils.  Nitrifica- 
tion, however,  was  not  restored  under  the  existing  field  conditions. 
It  is  probable  that  reinoculation  with  both  the  ammonifying  and 
nitrifying  organisms  gradually  took  place,  but  the  lack  of  aeration 
prevented  the  development  of  the  nitrifying  bacteria.  These  soils 
had  not  been  cultivated  for  two  years  previously  and  received  no 
tillage  during  the  time  of  observation.  It  is  not  possible  to  state  the 
temperature  to  which  the  soil  was  heated  in  these  instances.  An  ap- 
proximate test  applied  in  another  locality,  however,  indicates  that 
the  burning  of  small  brush  heaps  similar  to  those  burned  on  the  soils 
above  discussed  created  a  temperature  of  about  200°  C.  6  inches 
below  the  surface.  The  temperature  would  naturally  vary  greatly 
from  place  to  place. 

EFFECTS    OF   HEAT    ON    THE    ORGANIC    NITROGEN. 

Having  found  that  large  amounts  of  ammonia  are  formed  from  the 
action  of  heat,  a  study  of  the  organic  nitrogen  as  affected  by  heat 
seemed  of  interest.  It  is  well  known  that  ammonia  is  one  of  the 
cleavage  products  of  protein  hydrolysis.  It  is  also  known  that  in 
the  destructive  distillation  of  organic  nitrogenous  substances  ammo- 
nia is  one  of  the  decomposition  products.  It  was  observed  that  the 
amounts  of  ammonia  recovered  from  heated  soils  by  means  of  dis- 
tillation were  not  proportional  to  the  total  nitrogen  present,  but 
seemed  to  depend  largely  on  the  type  of  the  soil.  The  amount  of 
ammonia  obtained,  for  example,  from  soil  No.  335  was  very  much 
less  than  that  from  the  other  samples  studied  (page  32).  Ammonia, 
therefore,  was  probably  volatilized  and  driven  out  of  the  soil  to  a 
greater  extent  in  some  instances  than  in  others.  Soil  335  is  a  sandy 
soil  composed  very  largely  of  coral  sand  (CaCOs).  In  the  foregoing 
work  total  nitrogen  determinations  were  not  made.  Hence  it  is  im- 
possible to  correlate  the  rise  and  fall  of  ammonia  with  losses  of 
nitrogen. 

In  order  to  throw  further  light  on  these  questions  total  nitrogen 
and  the  several  groups  of  nitrogen  compounds  rendered  soluble  in 
boiling  hydrochloric  acid  were  studied.  For  this  purpose  the 
method  of  Hausmann1  as  modified  by  Osborne  and  Harris2  was  ap- 
plied. This  method  was  devised  for  a  study  of  protein  chemistry, 
but  has  been  previously  used  by  Jodidi  and  others  in  studying  the 
organic  nitrogen  of  soils.3 

Ztachr.  Physiol.  Chem.,  27  (1899),  p.  95.  Jour.  Amer.  Chem.  Soc,  25  (1903),  p.  323. 

Michigan  Sta.  Tech.  Bui.,  4  (1909);  Iowa  Sta.  Research  Bui.,  1  (1911). 


35 


In  this  study  total  nitrogen,  nitrates,  ammonia,  amids,  diamino 
acids,  and  monamino  acids  were  determined.  Nitrates  and  ammo- 
nia were  determined  in  the  soil  directly,  while  the  groups  0f  organic 
compounds  were  determined  in  solutions  obtained  by  boiling  50 
grams  of  soil  with  750  cubic  centimeters  of  hydrochloric  acid  under 
a  reflux  condenser  for  10  hours,  as  outlined  by  Jodidi,  filtering, 
and  making  the  filtrate  up  to  1  liter. 

The  organic  nitrogen  of  soils,  having  at  one  time  been  bound  up 
largely  in  proteid  combinations,  may  reasonably  be  expected  to 
yield  hydrolytic  products  similar  to  those  formed  from  protein. 
But  little  is  known,  however,  regarding  the  specific  hydrolysis 
induced  by  the  microflora  of  the  soil.  It  is  not  known,  for  example, 
whether  the  protein  molecule  as  a  whole  is  broken  down  with  the 
ultimate  liberation  of  ammonia  from  the  several  classes  of  protein 
cleavage  products  in  the  same  ratio  in  which  nitrogen  occurs  in 
them  or  whether  certain  of  these  groups  yield  inorganic  or  elementary 
nitrogen  more  readily  than  others. 

Samples  of  both  heated  and  unheated  soil  were  studied  in  this 
connection.  The  former  were  subjected  to  a  temperature  of  200° 
C.  for  a  period  of  two  hours,  after  which  the  same  treatment  and 
determinations  were  made  as  in  the  unheated  portions.  The  results 
are  recorded  in  the  following  table: 

Nitrogen  compounds  in  heated  and  unheated  soils. 


i 

to 
o 

i 

o 

a 

1 

2 

Ctj 

1 

£ 
S 
< 

Soluble  in  hydrochloric  acid. 

Composition  of  hydro- 
chloric acid  soluble. 

Soil  numbers. 

a 

< 

o 

a 

as 

«8 

o 

a 

as 

a  8 
o 

3 

o 

03 

'3 

o 

a 
a 
< 

W3 

1 

< 

o 

a 

—  « 

as 
p 

o 
a 

|| 

a  a 

o 

3 

Unheated: 

379 

P.ct. 
0.546 
.179 
.504 
.779 
.396 

.417 
.178 
.419 
.608 
.207 

P.ct. 

0.001 
.0001 
.0015 
.0045 
.0062 

.0 
.0 
.0 
.0 
.0 

P.ct. 
0.001 
.005 
.006 
.022 
.001 

.069 
.036 
.067 
.031 
.020 

P.ct. 
0.096 
.042 
.079 
.129 
.074 

.098 
.055 
.103 

.077 
.039 

P.  ct. 
0.  030 
.018 
.055 
.029 
.033 

.034 
.017 
.019 
023 
.022 

P.ct. 
0.298 
.100 
.240 
.363 
.125 

.168 
.044 
.092 
.079 
.028 

P.ct. 
0.426 
.165 
.381 
.558 
.239 

.369 
.152 
.281 
.210 
.109 

78.02 
92.  IS 
75.  59 
71.63 

60.35 

88.49 
85.39 
67.05 
34.  ,54 
52.65 

P.ct. 
0.23 
3.03 
1.57 

P.ct. 
22.53 
25.45 
20.74 

P.ct. 

7.04 
10.91 
14.43 

5.9 
13.80 

9.20 
11.18 

6.76 
10.95 
20.18 

P.ct. 

69.  95 

405 

406 

66.  06 
62.97 

428 

3.94i  23.12 
.41    30.69 

18.69!  26.56 
23.68   36.18 
23.84'  36.65 
14.76   36.66 
18.35    35.7! 

65.05 

447... 

52  30 

Heated: 

379 

4.">  S3 

405 

406 

28.95 
32.74 

428 

37.62 

447 

25.69 

Considering  first  the  unheated  soils,  the  nitrates  and  ammonia 
are  shown  to  constitute  a  relatively  small  percentage  of  the  total 
nitrogen  and  to  vary  greatly  in  the  different  soils  examined.  Soil 
447  was  found  to  contain  the  highest  amount  of  nitrates,  while  in 
No.  405  nitrates  were  present  to  the  extent  of  only  one  part  per 
million.     No.  428  contained  an  abnormally  high  ammonia  content, 


36 

while  Nos.  405  and  406  also  contained  many  times  as  much  ammonia 
as  nitrates. 

The  relative  amounts  of  nitrogen  extracted  by  hydrochloric  acid 
also  varied  greatly.  In  soil  No.  405,  92.18  per  cent  of  the  total 
nitrogen  went  into  solution,  while  No.  447  yielded  only  60.35  per 
cent  of  its  nitrogen.  Nos.  405  and  406  are  soils  that  have  been 
devoted  to  aquatic  agriculture  (rice  and  taro)  for  many  years,  while 
soils  379,  428,  and  447  have  been  subjected  to  dry-land  cultures. 

The  chemical  decompositions  and  hydrolyses  that  take  place 
naturally  in  the  organic  matter  of  soils  being  brought  about  largely 
by  biological  agents,  it  is  probable  that  the  range  and  types  of  such 
reactions  in  submerged  soils  are  somewhat  different  from  those 
taking  place  in  well-aerated  soils.  There  are  several  lines  of  reason- 
ing not  necessary  to  mention  here  that  lead  to  this  conclusion. 
From  this  point  of  view,  then,  the  biological  effects  on  soil  nitrogen 
may  reasonably  be  expected  to  be  different  in  the  two  instances. 
The  nature  of  the  organic  matter  originally  incorporated  with  the 
soil  probably  has  some  bearing  on  this  question  also. 

Among  the  several  groups  of  nitrogen  compounds  brought  into 
solution  by  hydrochloric  acid  it  is  noteworthy  that  the  amids  and 
monamino  acids  constitute  the  main  portion.  The  latter  comprises 
approximately  two-third©  of  the  total  nitrogen  dissolved.  It  should 
be  borne  in  mind,  however,  that  the  monamino  nitrogen  was  deter- 
mined by  difference;  that  is,  by  subtracting  the  sum  of  the  other 
groups  from  the  total  nitrogen  in  solution.  It  is  known,  however, 
that  this  difference  is  not  made  up  entirely  of  monamino  acids. 
Jodidi1  found,  for  example,  that  the  monamino  nitrogen  group 
in  Iowa  soils  was  made  up  of  from  40.12  to  92.11  per  cent  of  actual 
monamino  acids,  the  variation  in  this  respect  being  dependent 
in  part  on  the  treatment  to  which  the  soil  had  been  previously 
subjected.  It  is  of  interest  that  the  relative  amounts  of  amids, 
monamino,  and  diamino  nitrogen  in  Hawaiian  soils  were  found 
similar  to  those  of  soils  elsewhere. 

Turning  now  to  the  question  of  heat  as  affecting  soil  nitrogen,  it 
was  found  that  with  the  exception  of  No.  405  the  average  loss  of 
nitrogen  was  about  25  per  cent,  but  in  certain  soils  the  loss  was 
much  greater  than  in  others.  Soil  No.  447  suffered  a  loss  of  prac- 
tically 50  per  cent  while  No.  405  sustained  almost  no  loss  of  nitrogen. 
It  is  also  of  interest  that  the  reduction  in  the  amounts  of  nitrogen 
extracted  by  hydrochloric  acid  was  greater  in  two  instances  and  less 
in  three  than  the  absolute  loss  of  nitrogen  occasioned  by  heat.  In 
every  instance  enormous  increases  in  ammonia  and  a  total  decompo- 
sition of  nitrates  took  place.  On  the  whole,  the  absolute  amounts  of 
neither  the  amids  nor  the  diamino   acids  were  greatly  affected  by 

'Iowa  Sta.  Research  Bui.  1  (1911). 


37 

heat,  whereas  there  was  relatively  large  reduction  in  the  nitrogen  of 
the  monamino  acid  group  in  every  soil  studied. 

Heating,  therefore,  caused  a  loss  of  nitrogen  on  the  one  hand  and 
an  increase  in  ammonia  on  the  other,  and  the  decompositions  appear 
to  come  principally  from  the  monamino  acid  group.  The  amounts 
of  amids  in  soils  Nos.  428  and  447  and  the  diamino  acids  in  Nos.  406 
and  447  also  sustained  considerable  loss  from  the  heating. 

Regarding  that  portion  of  soil  nitrogen  remaining  insoluble  in 
hydrochloric  acid,  next  to  nothing  is  known.  By  again  referring 
to  the  table  (p.  35)  it  will  be  seen,  however,  that  the  heat  had  some 
effect  on  the  insoluble  nitrogen  compounds.  The  difference  between 
the  total  nitrogen  in  the  soil  and  that  extracted  shows  that  consid- 
erable reduction  in  the  insoluble  nitrogen  of  soils  Nos.  379  and  447 
took  place  by  heating,  while  there  was  a  gain  in  the  insoluble  nitro- 
gen of  soil  No.  428.  The  organic  matter  of  soil  No.  428  is  in  a  less 
advanced  stage  of  decomposition  than  that  of  the  other  soils  studied 
and  it  was  noticed  that  a  pronounced  charring  in  this  soil  took 
place  under  the  action  of  the  heat.  It  seems  probable  that  such 
charring  of  the  organic  matter  would  tend  to  protect  the  nitrogen 
bodies  in  the  interior  of  the  particles  from  the  action  of  the  solvent, 
thus  apparently  increasing  the  percentage  of  insoluble  nitrogen. 

SUMMARY. 

(1)  Twelve  different  soils  representing  a  wide  range  of  types  and 
agricultural  conditions  were  studied  with  reference  to  the  effects  of 
heating  to  100°  C,  to  250°  C,  and  to  ignition.  The  solubility  of 
all  the  mineral  constituents  except  sodium  was  determined,  using 
water  and  fifth-normal  nitric  acid  as  solvents.  The  effects  on  the 
nitrogen  compounds  were  also  investigated. 

(2)  The  results  showed  considerable  variation.  Neither  the  abso- 
lute nor  the  relative  solubility  of  the  inorganic  constituents  were 
effected  similarly  in  all  the  samples  studied. 

(3)  On  the  average,  drying  at  100°  C.  was  found  to  bring  about 
an  increase  in  the  water  soluble  manganese,  lime,  magnesia,  phos- 
phoric acid,  sulphates,  and  bicarbonates.  At  this  temperature  an 
increase  in  the  solubility  of  potash,  silica,  and  alumina  was  pro- 
duced in  about  50  per  cent  of  the  soils  examined,  but  a  decrease 
was  observed  in  the  solubility  of  these  elements  in  some  instances. 
The  solubility  of  iron  was  decreased  in  most  instances. 

(4)  Heating  to  250°  C.  or  ignition  produced  effects  on  the  solu- 
bility in  water  similar  to  those  brought  about  at  100°  C,  but  vary- 
ing in  degree,  these  being  sometimes  greater,  sometimes  less  in 
intensity  than  those  produced  at  100°  C. 

(5)  The  solubility  in  fifth-normal  nitric  acid  was  not  greatly 
affected  by  heating  to   100°  C,  but  in  some  instances  heating  to 


38 

250°  C.  considerably  increased  the  solubility  of  alumina,  manga- 
nese, potash,  and  phosphoric  acid  and  at  the  same  time  effected 
a  reduction  in  the  solubility  of  lime  and  magnesia.  Upon  ignition 
the  solubility  of  silica,  alumina,  potash,  phosphoric  acid,  and  sul- 
phates was  increased,  while  the  solubility  of  lime  and  magnesia 
underwent  a  corresponding  decrease. 

(6)  The  solubility  of  soils  used  in  aquatic  agriculture  is  abnor- 
mally high,  but  upon  drying  out  these  become  much  less  soluble 
and  approach  a  state  similar  to  that  existing  in  aerated  soils.  When 
such  soils  are  heated  after  drying  they  seem  to  undergo  changes  of 
the  same  order  as  are  produced  in  dry-land  soils. 

(7)  No  single  factor  is  sufficient  to  cover  the  solubility  effects 
resulting  from  heating  Hawaiian  soil.  On  the  other  hand,  the 
subject  is  very  complex  and  involves  many  factors.  Among  the 
more  important  of  these  may  be  mentioned  flocculation,  deoxida- 
tion  of  manganese  dioxid,  oxidation,  particularly  of  iron,  double 
decomposition,  dehydration,  and  the  attending  physical  alterations 
of  soil  films.  Such  alteration  would  destroy  film  pressure,  thus 
allowing  the  solvent  to  come  into  more  intimate  contact  with  the 
soil  constituents.  At  the  higher  temperatures  bicarbonates  become 
converted  into  normal  carbonates,  thus  effectively  lowering  the  solu- 
bility of  lime  and  magnesia. 

(8)  Nitrates  undergo  decomposition  with  heat,  a  decrease  in 
nitrate  content  having  been  found  to  take  place  at  150°  C,  while 
at  200°  or  250°  C.  practically  total  destruction  of  nitrates  took 
place. 

(9)  One  of  the  noteworthy  effects  of  soil  heating  is  the  production 
of  ammonia,  which  at  200°  C.  was  formed  in  abnormally  large 
amounts.  Soil  subjected  to  heat  from  brush  burned  in  the  field 
was  found  to  undergo  stimulated  ammonification  after  heating. 
Nitrification,  on  the  other  hand,  was  not  restored  after  the  lapse  of 
two  months. 

(10)  Heating  to  200°  C.  caused  a  loss  of  approximately  25  per 
cent  of  the  total  nitrogen.  A  loss  of  nitrogen  and  the  ammonia 
formed  by  the  action  of  heat  came  largely  from  the  monamino 
acid  group,  while  the  amids  and  diamino  acid  sustained  much  less 
loss. 

(11)  The  results  of  these  studies  are  believed  to  throw  important 
light  on  the  subject  of  soil  aeration  and  consequently  have  a  direct 
bearing  on  the  practical  question  of  soil  management. 


UNIVERSITY  OF  FLORIDA 

■■Mill 

3  1262  08929  1099 


